The ARS-1 shares the same rail interface as the SMB and the LMB Accessory Adapter. Two ball-pressure pieces on each side of the rail prevent an attached Accessory Rail Bracket ARB-1 from slipping off. It is compatible with all 3/8-16 interfaces which offer holes for the two securing pins. Uniquely, four different sizes of hex key can be used with the Accessory Rail Small without having to adjust it - 3,4, 5 and 5/32 will all fit perfectly. Length: 30mm/1.18”