These bullet guides are for the 7.62x39 Saiga and Vepr rifles. Installation of this guide allows your rifle to feed high capacity AK magazines. Shown below are the guide install kits shown with #8-32 drill & tap. (note: pics may not reflect actual geometry)
Round Trunnion Kit
Flat Trunnion Kit
Round Trunnion Left, Flat Trunnion Right
The front trunnion is the block of steel riveted in the front of the receiver that the barrel is pressed into. The shape description comes from the shape of the area immediately below the chamber face.
Trunnion with Rivet Hole drilled (round or flat)
If you have a rivet hole drilled in your trunnion, select the rivet guide kit (X39RTGR or X39FTGR) which includes a screw and a nut.
The bullet guides have a machined barrel relief on the front which tucks under the barrel face. On the round guide, the hole is offset on the guide, with the hole located more to the right. The holes goes bottom dead center in the 6 o'clock position. The pic on the right shows the guide installed properly. Note the right hand edge of the guide does not go to the right of the step in the chamber face.