Trijicon RMR footprint, or simply RMR footprint, is the most commonly used footprint standard. This footprint is most popular among optics designed for full sized or compact pistols.

You can recognize this footprint by two details:

• it has 2 sockets in the front corners,
• the sockets are cca 23mm 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 Trijicon RMR 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 "Trijicon RMR footprint" that also has your handgun in the compatibility list.