IIRC, the Lyman peep sight that mounts in the factory d&t holes on the very rear of the receiver is the R-12. Mable's also made a similar peep sight that installed in the factory d&t holes, but I don't recall what the model # is. The Lyman is a nice little unit, I had 1 on a Remington 12CS in 22 Remington Special that my Father kept around to shoot 'chucks in the garden. It is a rifle that I wish I hadn't sold, but thems the breaks!
Jeff
