Freeze plugs 1983 xj6

Can anyone tell me the physical size of the freeze plugs in the head. The three in the valley, just making sure I can get the correct size to the mechanic so I don’t have to wait for them to source parts. ( new battery this week, water pump in my 350 SL merc., they come in three’s so enough is enough!)
I’d do it myself but with only one arm working I just know it would be a disaster and eight weeks to do the merc. and I’m running out of cars to drive!