I have a Marksman Monarch, bought second-hand and came without a sight, though there was an attachment block on the riser. I bought a Cartel Focus and found that the screws were too big for the threads in the Monarch. I got round this by using the screws from the original block, though I had to shorten them as the Cartel block is thinner. The problem I have is that the screws have a tendency to loosen with vibration and as they are slotted heads, the frequent re-tightening is wearing the slots. I would like to replace these with hex-head screws but I do not know what the thread is in the Monarch riser - does anyone know, please?