Can anyone tell me the size of the RB block cam freeze plug that goes into the back of block between the screw-in oil galley plugs?

My machinist and I must have had a small communication breakdown when I asked him to leave out the oil galley plugs, 'cuz I realized while washing the block that the cam plug wasn't installed, either.

It'll be easier to stop by the parts store that's 5 minutes down the road than make a trip back to the machine shop, if someone can tell me the correct dimension for the missing plug. Thanks.