These Shock-proof Rail mount from Cynosure are made from the finest quality hard-steel with steel Allen screws for longer life. Shock Proof mount is used to avoid sliding of your optical instrument while firing. Each scope clamp has four top screws to firmly hold the scope and comes with a pair of tube dia reducers to hold scopes of smaller dia. The default diameter is 30mm and with the reducer, it decreases to 25.4mm. Shock-proof Rail Mount is best suitable for airguns and firearms of high power. These can easily withstand the recoil pressure from the weapon with the help of the stopping screw provided at the bottom of one of the mounting clamp.