GLOCK Modular Optic System (MOS) Configuration

GLOCK engineers have developed the Modular Optic System (MOS) configuration to simplify mounting of popular optical sights.

Optical sights improve the accuracy at both long and short range, enabling faster target transition and quicker sight acquisition of your target. The MOS configuration is the best choice to hit your target. 

Slimline MOS
The Slimline MOS pistol models have slide cuts designed for specific micro-optics and do not need Adapter Plates.

Standard MOS
GLOCK pistol models in standard MOS configuration come with four numbered GLOCK MOS Adapter Plates. This excludes the G20 Gen5 MOS, G21 Gen5 MOS, and G47 MOS. With the introduction of these three new models, they will only come with one adapter plate that will fit the following RDS: Trijicon®, Ameriglo®, and Holosun® (except 509). If your selected optic is not compatible with any of the above, additional options are available on the online GLOCK store.



G20 Gen5 MOS

The standards of performance and reliability can’t be beat now with the option to add an optic to the new G20 Gen5 MOS.

G21 Gen5 MOS

With the new addition of the .45 AUTO in the Gen5 lineup, the G21 Gen5 MOS delivers improved accuracy, light recoil, and now has the option to install an optic.


Trusted by the United States Customs and Border Protection, the G47 MOS offers reliable performance, especially with the option to add an optic.

What’s the difference in reflex optics and standard iron sights?

Reflex Optics: You can look through the reticle and focus on the target and alignment of the dot. Optical sights are popular in competitive shooting and are becoming increasingly common for home defense and target shooters.

Standard Sights: You must align the front and rear sight with a hard focus on the front sight.

What’s the importance of dot size?

Large dots: Easier to see in close range and bright light situations.

Small dots: Better for long distance targets and low light situations.

MOS difference


Step 1: Remove the GLOCK Cover Plate.

Step 2: Select the appropriate GLOCK MOS Adapter Plate and place it in the correct position.

Step 3: Tighten the 2 Torx® screws to fix the GLOCK MOS Adapter Plate on your GLOCK MOS pistol.

Step 4: When the GLOCK MOS Adapter Plate is completely mounted on your GLOCK MOS pistol, install the optic system according to the directions of the manufacturer.

To download the GLOCK MOS Instruction Guide, CLICK HERE

Step 1: Remove the GLOCK Cover Plate.

Step 2: Use the M4x8mm flat-head screw to mount the optic on your GLOCK Slimline MOS pistol

Step 3: Only shoot your GLOCK MOS pistol with the correctly installed GLOCK Cover Plate or optic system

WARNING: If the thread length of the screw exceeds 8mm, it may cause damage to the weapon and/or may cause malfunction. GLOCK recommends a periodic check of Cover Plate or optic screws to ensure tightness.

To download the GLOCK Slimline MOS Instruction Guide, CLICK HERE


Learn more about correctly installing the MOS with adapter plates on your GLOCK by watching the instructional video:
GLOCK MOS Installation Instruction

The following GLOCK pistols are available in Modular Optic System (MOS) configuration