This .500” thick Reversible Picatinny Rail is intended for the assembling of target scopes on 10/22 rifles. In its normal position it extends over the barrel. Also, as one of its unique features, the rail can be assembled in reverse so it extends more in the rearward direction and by doing so, the scope/optic can be brought back (in cases like scopes with short eye-relief, some bench-rest positions, stocks with large length of pull, shooters with small frame - children). When reversing the rail, no extra holes have to be drilled in the receiver, as the specific hole pattern in the rail takes care of that and makes possible that it can be assembled in reverse. Another unique feature of our design regards the optional extra strength and rigidity in holding the rail onto the receiver. For this, your gunsmith will simply drill and tap 2 additional holes #6-48 tpi into your Ruger OEM receiver (this is not required in the case of our DAR-22 receiver, as it already has the extra holes). 6160 Aluminum. Anodized Black. Package includes 6 screws #6-48 tpi. The screws are 1/4" long (but if you intend to use this rail on our DAR-22 receiver, we suggest you take advantage of the receiver's thick top and purchase the #6-48 tpi 5/16" screws from our on-line store because they are longer and they provide for a better engagement).