No, I would say that a prior owner swapped it out for whatever reason. The square plug is most common in plumbing applications due to the heavy use of pipe wrenches. It cannot be inside out as this plug is an NPT thread which is tapered.

 

ok, thanks, i did not know. so, would auto zone or advance carry a stock replacement plug so i can correct this?

 

I do not think it is something that needs correcting unless you do not get the tools to properly remove/reinstall the current plug. Any hardware store should have a plug that will work. It will likely have a hex instead of a square bore though.

 

ok, thanks

 

So...if this seems to be a household plumbing fitting...made for use with a pipe wrench and/or crescent wrench....why not use the pipe wrench and/or crescent wrench to get it off?

 

Access. The webs on the diff make it near impossible to get a wrench on it. If the square protrusion is long enough, you may be able to use an open ended wrench on it, but I am sure you have already tried something like that.

For illustration purposes, here is a picture of the diff where the fill plug is:

 

NEW PLAN. Gear wrenches. Everyone could use some nice gear wrenches. Espeically you, with your oddly replaced fill plug with limited access.

 

yup, thats how it looked when i changed my friend's diff oil. i figured that mine looked like that so i got all the stuff i need before i looked at it. well, i am going to run out to the parts store this morning to get a either an 8 point socket or some square tubing. thankss for all the help guyz. swartlkk, i read your diff service to make sure i was got all the right stuff and what not, just wondering, did you special order the diff cover or the dealership have it in stock? anf, how come you didn't paint the cover?

 

Dealer had to order it. They had it the next day. The gaskets they had in stock. I did not paint it because I did not have time.

 

ok, thanks, i went out and got a new cover today and i figured out the the fill plug was an 11/16. so i am finally set now. thanks for all the help guys.