EXPLAINING THE ISMS MODEL MARKINGS

Most items from Spuhr are marked with a model number and a batch number. When ordering please refer to the model numbers.

Scope mounts are marked with a model number consisting of two or three letters followed by four digits. However, there are three exceptions to this rule where there is a total of five digits as well as some models featuring a suffix.

The batch numbers consist of four letters. Old batch numbers consisted of a single letter followed by four numbers; for example M-1204 or M12/04, where the numbers indicate year and month. 


The initial letters identify the type/firearm/rail the mount is designed for:
QDP - Quick Detachable mount Picatinny
SP - Scope mount Picatinny
ST - Scope mount TRG (17 mm dovetail)
SR - Scope Rings (separate rings for Picatinny rail)

The first digit identifies tube diameter:
3 - 30 mm tube
4 - 34 mm tube
5 - 35 mm tube
6 - 36 mm tube
7 - 40 mm tube

The second digit identifies tilt:
0 - 0 tilt
3 - 3 MIL/10.3 MOA
6 - 6 MIL/20.6 MOA
7 - 7 MIL/24 MOA tilt
8 - 13 MIL/44.4 MOA
9 - 9 MIL/31 MOA

Note: The SP-61602 and SP-41808 feature two digits for tilt: 16, indicating a tilt of 16 MIL/55 MOA, and 18, indicating 18 MIL/61.8 MOA. First run of SP-4803b had 11 MIL/40 MOA tilt.

The third digit (if other than 0) is for special versions:
1 - Cantilever mount
2 - Extended-length cantilever mount
3 - Short rear top cover for the S&B Ultra Short
4 - Medium-height cantilever mount

The fourth digit identifies height:
1 - 30 mm / 1.18"
2 - 38 mm / 1.5"
4 - 48 mm / 1.89"
6 - 34 mm / 1.35" (except for on Cantilever mounts)
8 - 44 mm / 1.73"

Note: The height is always measured from the top of the rail to the centerline of the optics. On a tilted mount the measurement is made at the back plane of the rear ring.

B suffix
Some older mounts featured a B suffix following the model number. In the ISMS line this indicates an extra-long mount for scopes with extended length erector housings, such as the U.S. Optics TPAL and the NightForce B.E.A.S.T.

C suffix
Some mounts feature a C suffix following the model number. This denotes a Gen3 mount which has either an updated side clamp design or (for all 34 mm mounts) an increased distance between the rings, using an A-40B rear top cover, or both.

M suffix
Models with an “M” suffix indicate an extra‑strength mount engineered for demanding, heavy‑duty applications. This reinforced series was developed in direct response to feedback from our professional customers.

Cantilever Mounts
We currently offer three heights for our cantilever mounts. We offer two types of cantilever design: a 40 mm/1.57" cantilever and a 70 mm/2.75" extended cantilever. Mounts with a 1 or 4 as a third digit in the model number feature the 40 mm cantilever, whereas mounts with a 2 as the third digit feature an extended cantilever.