MAG|Couplers™ use a series of teeth on both sides of the coupler to hold the coupler tight to the magazine body. 

They are designed to be very tight when installed and may require some force when being slid onto the magazine body.  This fit ensures a solid pair of coupled magazines supporting the recoil of the platform.  

A small amount of liquid dish or hand soap applied to the teeth of the coupler will greatly aid in the installation.