HSS is fully compatible and a confirmed fit into Ruger MK III and MK II series pistols (except 22/45 versions).

  • MK II was manufactured from 1982-2005, followed by MK III manufactured through Dec 8, 2016.


HSS is compatible with MOST earlier Ruger Standard and MK I pistols. 

These were manufactured from 1949-1982.  Most people with Ruger Standard and Mk1 pistols have installed the HSS with no problems at all.  See 1965-1976 exceptions below.


HSS will fit Volquartsen Scorpion pistols that are not 1911 style (they are 22/45 versions).


HSS will fit AMT Lightning pistols (unauthorized clones of the Ruger MK II).

Ruger Manufacturing Inconsistencies 1965-1976

In 1965-1969, Ruger had manufacturing inconsistencies with the "perpendicularity" of, the "sear spring retaining pin", commonly referred to as the "cross-pin" on this website.  The right end of the cross-pin may be a few thousandth of an inch higher (towards the top of the gun) than the left side.

In 1970-1976, Ruger had manufacturing inconsistencies in the clearance under the "sear spring retaining pin", commonly referred to as the "cross-pin" on this website.  A minimum clearance space under the cross-pin of 0.036 inches is required to install the HSS.

As reported by customers, these problems have been found in the following Ruger pistols:​


Summary of possible fitting problem for MK I pistols (1965-1976)

1965-1968 sn 334991 was incompatible, sn 412517 was compatible, but sn 445xxx was not. For sn 334992 and above: minor fitting MAY or MAY NOT be required. (Pistol cross-pin may not be perpendicular to handle.)

1970-1976 sn 10-58067 to 13-49225 need fitting or may be incompatible.  (HSS slot needs to be made deeper)


TEMPORARY NOTE FROM HSS CORP: The HSS normally needs about .035 inch clearance under the cross-pin.  We have a few HSS items with deeper cut slots, that may fit some MK I models from 1970-1975. Call for more info on special fitting of  these. Tom @ 256-527-3527




All other Ruger MK I and Ruger Standard Pistols should be compatible​.  If you have more information that can help narrow the "problem range", please let us know.  Thank you.


To see what year your pistol is, go to the Ruger website:

We have a money back guarantee on our HSS.  If you would like to try the HSS on one of these earlier pistols, we will gladly refund your purchase price if it does not fit.  Just let us know the details about what pistol and what year it did not fit.


HSS is not compatible with any Ruger MK 22/45 pistol.

All Ruger 22/45 pistols (both Mk III and MK II versions) have an entirely different handle, a more vertical handle, which is modeled after the popular model 1911, 45 caliber, pistol.   All of these pistols do not have a cross-pin and use a different kind of sear spring, so the HSS is not compatible with any of these. 


HSS is not compatible with the new Mk IV models.

The MK IV models began to be sold in Dec, 2016.  These have a "tip-off" barrel design, wherein the barrel can be rotated off of the frame, after depressing a release button.


Typically 1965-1968 models only need a very slight widening of the upper right corner of the HSS cross-slot.  This can be done quickly with a small jeweler's file (file info below).  Also, putting a taper on the right end of the cross-pin helps realign the cross-pin back into the hole.


There are SOME pistols in this 1970-1976 range where it would be necessary to take a significant amount of material off of the HSS to make the slot deeper.  Others, only need a little material removed.  You will need to measure the clearance under the cross-pin to evaluate (info below).


Also, the HSS is a coated steel, good to 18 hours of salt water immersion without any noticeable depreciation.  If you file some material off the HSS, be sure to spray paint the newly exposed steel.  There is no temperature or vibration or pressure or other problem in the handle area that would overcome a thin layer of spray paint on the HSS.  Once assembled, the HSS touches no moving parts, so there are no moving parts to rub the paint off either.  


The normal clearance under the cross-pin is usually at least 0.035 inch.  You can probably file the HSS thickness under the slot down to 0.025 inches and the HSS still be plenty strong, since there is no bending stress being placed upon it.  You can measure the available clearance under the cross-pin in your pistol by using an automotive feeler gauge of the "bent wire" type, typically used for spark plugs, etc.  (PS: the reason that we do not make the HSS thickness under the slot 0.025 inches is that it might "rattle" in many pistols.)  Note: a small round file that fits the HSS slot is available at Lowe's stores as part of a small 6-piece set, item number 0159850, for $3.98. 


In any case, we will refund the purchase price of the HSS for any reason, IF it has not been modified.

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