Shield RMSc / or simply RMSc footprint is considered standard for compact and subcompact pistols.

You can recognize this footprint by two details:

• it has 4 sockets - each in one corner,
• the closer sockets are 17mm from each other,
• the more distant sockets are cca 33mm from each other.

If you have classic handgun, you need to be searching for a red dot mount which replaces rear sight in the dovetail cut: red dot mount with Shield RMSc footprint:

• Red dot mounts for Beretta models
• Red dot mounts for Canik models
• Red dot mounts for CZ models
• Red dot mounts for HK models
• Red dot mounts for Glock models
• Red dot mounts for HS Produkt models / Springfield Armory models
• Red dot mounts for Sig models
• Red dot mounts for Tanfoglio models
• Red dot mounts for Taurus models
• Red dot mounts for Walther models
• and other

Make sure to search for mount with "Shield RMSc footprint" that also has your handgun in the compatibility list.