I'm changing the fluid out in the differential of my 65 Valiant while I'm working on some other things under the car. The fluid was nasty but not the worse I've seen, no telling how long it's been in there. I just removed the whole cover because I couldn't tell what I needed to get the fill plug out. The whole rear axle is covered in mud so I had to scrape just to get to the cover bolts. I can't tell if the fill plug is a 1/2" ratchet head or a big hex head. I saw in the 65 parts catalog it's a 7/8-18 thread size plug. What tool do I need to unscrew it ratchet or what size hex head?