so I had a plug in this hole when I deleted the black box. the plug fell out and I'm trying to find out the size so I can get a new one. anyone know? it's the one with the nipple coming out of it between piston 1&2

 

Im pretty sure that hole is not threaded...

 

it is threaded. I'm looking at it on my block right now.

 

B18?

 

Oh, sorry, i read wrong... I thought you meant the big hole at the bottom lol.

Im not 100% sure, but it is probably 1/8" BSPT. You could try an 1/8" NPT plug.

 

just fyi, the #1 cylinder is in the left of your picture.