This article will review the SHIS (Standard Headset Information System). This nomenclature is designed to simplify ordering replacement headsets. The article will also review the new headset machining tools from Park Tool.

There have been new and innovative headset design standards on the market for several years. However, there has been no consensus on naming these standards. Manufacturers tend to use proprietary names such as "Orbit Z", "NoThreadSet", "Zero Stack", "Hiddenset", etc.  As a result there can be several names for the same headset standard. This produces confusion among consumers, retailers, mechanics, and even bike manufacturers.

As a result of this confusion, a group of companies have developed a new system to consistently name these standards. This new system of nomenclature is known as the Standard Headset Information System, or SHIS.

The SHIS is not a new type of headset. It is a way to describe headsets and to bring organization to the discussion of different standards and how they fit the bike. Manufacturers, distributors, and retailers are now spreading this system. The SHIS requires some basic inspections and measurements. Using the SHIS terminology will then allow you to select the correct headset and to easily compare headsets between manufacturers.

The SHIS terminology consists of a two-letter code followed by numbers referring to the sizing of the frame or fork. Below in example #1 is the SHIS terms for a particular headset with descriptions of what the terms mean.

Figure 1. SHIS coding example (Example #1) with explinations of the various term parts

The SHIS may also be written for a complete headset (upper and lower) as ZS44/28.6 | ZS44/30. The upper and lower stack are separated by the "pipe" mark, looking like a vertical line: |

The headset example #1 might currently be listed in catalogs or website as any of the following terms: 

• 1-1/8” internal headset
• 1-1/8” Orbit Z
• 1-1/8” InSet, low-stack
• 1-1/8" ZeroStack
• Logic Zero Press Fit 1-1/8"
• Flat44 for 1-1/8" semi-integrated
• Zero Superlogic
• Hidden Cup Headset

These model names, as well as other fanciful titles, are actually interchangeable with one another. However these sundry monikers would not lead anyone to assume they are the same standard. This illustrates the need for a common system of description, and that is exactly what the SHIS is all about.

Like any new language, the SHIS requires some decoding. We will address each part of the SHIS terminology and what it means. The first two letters are code for the headset type. There are three basic types of headsets, the external cup (EC), the internal headset (ZS), and the integrated headset (IS).

EC
The external cup headset is the conventional or traditional pressed headset (figure 2). The bearing races sit outside the head tube. The SHIS designation "EC" is used for either threaded or threadless steering columns.

Figure 2. EC type headset, here installed with a threaded column and headset locknut

ZS
The internal headset uses bearings that sit below or at least flush with the head tube (figure 3). This system is also called Zero Stack, or semi-integrated.  There is a removable cup that holds and supports the bearing in the head tube.  The cup uses the top or bottom edge of the head tube as a stop, and the cups are purchased as part of the replacement headset.  The internal headset in the SHIS system is abbreviated as "ZS".

Figure 3. A cross section of a common ZS headset

IS
The integrated headset systems bearings that are supported by specially shaped headtubes (figure 4). The holder for the bearing is part of the frame and is not removed as part of headset service. A cartridge bearing slips into these "cups" or supports, and is simply lifted out for replacement. There is no bearing or cup contact with the face of headtube. The bearings rest on angular contacts inside the headtube. In years past, there were two different standards for the bearing contact angle for the integrated system, which were the 36-degree and 45-degree contacts. The 36-degree standard is now considered obsolete and the current standard is the 45-degree contact. Because the 36-degree frames are not being produced, the angular contact is not called out and is assumed to be 45-degrees for new headsets. Integrated headsets in the SHIS system are abbreviated as "IS".

Figure 4. Headtube for an integrated headset

Headtube Bore Diameter
The second number after the two-letter code refers to the headtube bore diameter. These are given in whole millimeters, and should be considered as a code, not an exact measurement. This is similar to naming threaded fasteners. For example, a common bicycle thread is the M5, called a 5-millimeter bolt. However, the actual size can be from 4.8mm to 4.85mm. It is simply agreed to call the thread M5 to simply the system.

To give an example with headset standards, the bore diameter external cup JIS headsets in the one-inch standard use a 29.8mm bore, but the SHIS code is EC29. The external cup "pro" or "euro" standard for the one-inch headset uses a 30.2 cup for a bore of 30mm. The SHIS for this standard is EC30.

Table #1 below outlines the traditional or legacy names for the EC cups and the cooresponding SHIS name. Table #2 outlines the more modern ZS systems, and Table #3 outlines the IS systems.

Table #1- SHIS for External Cup (EC)

Table #2- SHIS and legacy names for the Internal Headset (ZS)

Table #3- SHIS for the Integrated Headset (IS)

Steering Column- upper section
For the upper stack SHIS, the two-letter code and bore numbers are followed a forward slash ( / ) and then the column diameter. This is the outside column diameter where the stem clamps if it is a threadless fork. For threaded columns, it is the OD and is then followed by the threads per inch, abbreviated as tpi. For the common one-inch threaded headset, this would appear as 25.5-24tpi.

In example #1 in figure 1 (ZS44/28.6) the 28.6 is the common 1-1/8” fork diameter in metric. The stem must match this to clamp properly. This number in SHIS is the only one where there is a decimal. If the headset is available without the bike, measure the inside diameter of the top cap and consult Table 4 for the appropriate column size. There are no column standards that are close in size.

Table 4- SHIS Steering Column

For any threaded fork column, the diameter is followed by a dash and then the threads per inch or the pitch. For example, the common 1" threaded steering column is 25.4-24tpi. If there is no call-out of "tpi", it is assumed the column is threadless.

Fork Column- crown race
The lower stack SHIS terminology is similar to the upper stack but it will also include a reference for the crown race. The codes and bore sizes are those seen in Tables #1, #2 and #3. In Example #1, ZS44/30, the "ZS" tells us this is an internal type headset, and the 44 is again the bore size standard. The forward slash here is followed by the crown race press standard, in this case it is 30. The fork intended for this bike is a straight 1-1/8" column, not a tapered fork.

See Table 5 for SHIS names for the crown race. Note that the 1-3/8" crown race is an integrated system. The crown race shape is machined directly onto the fork, and there is no pressed race installed on the fork.

Table 5- SHIS Fork Crown Race

The SHIS becomes very useful when there are mixed headset standards on the bike (figure 5). The use of a tapered steering column is becoming more common, and a bike may have one headset standard at the top and a different standard and size on the bottom. It is also now possible to have two different types for upper and lower headtubes. For example a bike might have a ZS at the upper headtube and a EC for the lower.

Figure 5. A tapered lower fork column

Table 6 below shows just some of the possible combinations of sizing with the EC (external cup) systems.

Table #6 - Possible EC combinations

The ZS type headsets can be found on bikes with different upper and lower bore diameters (figure 6). There may also be bikes with a ZS headset type in one part of the headtube and the EC headset in the other part. Table 7 below lists some of the possibilities.

Table #7- Possible ZS combinations

 
Figure 6. A tapered headtube with different sizing for lower and upper headtubes

The IS types may also be mixed with different upper and lower bore diameters. There are also some sizes that are used exclusively on the lower headtube only. Table 8 below lists some of the possibilities.

Table 8- Possible IS combinations

Stack Height = H (optional)

Headset manufacturers may also include the stack height for more advanced SHIS terminology. This is abbreviated as "H" followed by the stack height in millimeters. The stack height "H" will follow after other SHIS sizing terms. Stack height is simply the amount of fork column the headset will take up or occupy. It is the amount the headset extends beyond the headtube. Stack height is listed separately for upper and lower stack. All headset types have some amount of stack height (figure 7 and 8).

Figure 7. An upper headset assembly with a 16mm stack height.
The full SHIS listing would read ZS44/28.6 H16

Figure 8. Lower stack external cup with 13.7mm stack height.
The full SHIS listing would read EC34/30 H13.7

SHIS EXAMPLES

Example #2: A common headset on many mountain bikes is sometimes referred to as a "Traditional 1-1/8 threadless cup" headset. The OD of the pressed cups measures 34mm (figure 7). The steering column is 26.8mm  (1-1/8"), and the crown race ID is 30mm. In the SHIS, this headset is written as EC34/28.6 | EC34/30.   This headset is for frame with an external cup design headtube with approximately 33.8-33.9mm ID. The steering column is 28.6mm, and a crown race of 30mm. It is intended for a straight fork, not a tapered fork. Any headset with the same SHIS would fit the bike as would headset in example #2.

 
Figure 7. EC34/28.6 | EC34/30 headset, (Example #2)

Example #3: Figure 8 is an internal style headset, with both bearings sitting inside the headtube, but held by pressed cups. This is the ZS type. The upper cup measures 44mm. However, the lower cup measures 56mm. The inside of the fork crown race is 39.9mm, but the steering column top is 28.6mm. This must have a tapered steering column. The SHIS for this system would be ZS44/28.6 for the upper, and ZS56/40 for the lower.

 
Figure 8. ZS type in mixed sizing, SHIS would be written as ZS44/28.6 | ZS56/40 (Example #3)

Example #4: The headset in figure 9 is again the ZS type.  The upper cup measures 44mm, and the inside of the top cap for the column is just over 28.6. The upper is then ZS44/28.6.  The lower cup is 49.71mm, and ZS type. But the fork crown race is 30mm, making the lower SHIS ZS49/30.  The headtube is tapered, but the fork is not, it is straight with the typical 30.1mm crown race seat. The lower headset acts as a reducer for this straight fork. The frame was made to accept a tapered fork, but this particular headset choice allows the use of the common 28.6mm column straight fork (1-1/8" fork). The bike would accept the larger SHIS 40 lower crown if the fork and lower headset were changed.


Figure 9. A reducer headset, ZS44/28.6 | ZS49/30 (Example #4)

Example #5: The frame in figure 9 has machined bearing holders directly in the frame and consequently is the IS type. The ID of the upper bore is 42mm. The fork column was 28.6. If no fork was available, measure inside the top cap from the headset. For this bike the upper headset SHIS would be IS42/28.6. 

 
Figure 9. Integrated system in the upper headtube, IS42/28.6 (Example #5)

Conclusion & Summary

The SHIS is a useful system to compare the fit of different models and brands of headsets. If two headsets' SHIS names match, they will interchange and fit the same bikes. The system will result in less confusion as bike manufacturers, distributors, and retailers begin listing frames and components with SHIS terminology.

Headsets may be purchased as a combined upper and lower set. However there are bikes with mixed standards, and headset may now also be purchased as an upper or lower assembly only. Once the SHIS system is fully in place, understanding headset fit and ordering headsets will become more organized and easier comprehended.

Summary of the SHIS Code System
The SHIS is a coded system of letters and numbers. Download a summary of the sizing of the SHIS here.

Headset Types
EC- external cup types, bearings above (or below) headtube face
ZS- internal or zero-stack type, bearing level or inside headtube face, but with removeable cup holder
IS- integrated type, bearing level or inside headtube, holder is part of frame design and not replace with service

Bore Diameter-upper stack
The upper stack two-letter code seen above is followed directly by a number representing the bore diameter (inside diameter) of the intended frame.

Column Diameter (at top of column)
The upper starck bore SHIS is followed by the " / " mark and then by a second number representing the top of the steering column diameter. If it is a threaded column it will be followed by a dash mark and the thread per inch if a fractional thread, abbriviated as tpi.

Bore Diameter-lower stack
The lower stack begins with the two-letter code seen above and is followed directly by a number representing the bore diameter (inside diameter) of the intended frame.

Crown Race
The lower bore SHIS is is followed by the " / " mark and then a second number representing the fork crown race inside diameter.

Stack Height
There may also be listed at the option of headset manufacturer for either upper or lower SHIS numbers the letter "H", followed the stack height in millimeters.

Related Headset Tools

Park Tool has added new tools for the machining and preparation of the headset fit in the frame. Only professional mechanics and frame builders should use these tools.

#788 Reamer in 43.95mm

The #788 Reamer is used for the ZS44 or EC44 standards, and is used with the 690-XL facer.The 788 includes a spacer the will change the depth of the reamed hole. In the "shallow cut" arrangement, the #788 will cut about 9mm deep into the headtube, just enough for most ZS44 headsets. There are in fact some headtube frame designs will not permit deeper cutting without damage to the frame. Place the spacer between the locking nut and the #788 reamer for cutting headset with minimal insertion (figure 10).

Figure 10. #788 reamer and wash installed for a shallow cut into the headtube

There are frame the use a deeper cut into the headtube, such a some EC44 designs. These require a full depth of cut of 15mm. Place the spacer between the 690-XL facer and the 788. This extends the reamer deeper into the headtube (figure 11).

Figure 11. The 788 reamer and spacer arranged for a full 15mm deep cut

It is possible perform facing only on the headtube without reaming using the #768 pilot and the 690-XL facer. (figure 12).

Figure 12. The facing only option using the 768 pilot

#789 Reamer in 55.95mm

The 789 Reamer is used for the ZS56 or EC56 standards. It cuts down to a depth of 15mm (figure 13). This requires the use of the 690-XXL facer for the large headtubes.

Figure 13. 789 reamer for the large ZS56 or ES56 standard

It is possible perform facing only on the headtube using the #790 pilot and the 690-XXL facer (figure 14).

Figure 14. The facing only option with the 790 Pilot and 690-XXL facer

The oversized headset in the ZS and EC types require the use of the #750 Centering Cone Adaptor to use the HTR. The 750 fits over the quick release tension cone of the HTR (figure 15).

 
Figure 15. #750 cone in place