1 & 5 - M4 socket head screw
4 - is M3 on the older shotguns and M4 on the newer recent ones.

The others don't need to be replaced.

You will have to shorten screws 1 & 5 with a grinder or dremel so they don't protrude through the receiver. Pull the trigger guard and can see how much to shorten them.

GC

 

Finished - thanks for the specs!

I did need to make two trips to the corner hardware store because a very similar size SAE bolt got tossed into the M4 bolt bin. Other than that clearly it's an easy switch. However that windage lock down screw sure is a tiny puppy. Put a bit of LocTite on that because I doubt I could easily source a replacement for it.

Felt good to really torque them down without fear of stripping the head or slipping and taking a gouge out of the finish.

 

It looks much better the socket screws. I have the same screws on my 982. Be careful and don't over torque them and break them off.

GC