Rear differential fill plug specs

[cropduster]

Hello,
The rear differential fill plug (square drive 3/8) on my Explorer is starting to round off. I'd like to have a replacement handy for the next time I check the fluid level. I had no luck searching for it on auto parts websites, and I'm pretty sure the guys at the local dealer will be of no help.
Is it a standard threaded plug that I can buy on any auto parts store? Or should I try my luck at the local junkyard?

Thanks for your help.

 

[drdoom]

I have purchased one for the transfer case at Advance (just a standard plug), but I'm not sure about a 3G rear differential.

 

[imp]

Hello,
The rear differential fill plug (square drive 3/8) on my Explorer is starting to round off. I'd like to have a replacement handy for the next time I check the fluid level. I had no luck searching for it on auto parts websites, and I'm pretty sure the guys at the local dealer will be of no help.
Is it a standard threaded plug that I can buy on any auto parts store? Or should I try my luck at the local junkyard?

Thanks for your help.

Most fill plugs (not all) have square male heads; some have square or even hexagonal female sockets. I have seen them sized from 1/2-inch standard pipe thread size to 3/4-inch.

But tell me now, given the fact that pipe threads are TAPERED to promote sealing, how would you tell one in Standard SAE size from Metric? Has anyone seen a metric pipe size, either a chart or real part? Gotta be one!