Block Drain Plug Size 97-98

Well I was trying to install an temperature sending unit today and took out the drain plug for the block of the drivers side of a 97 year 4.0. A torx 50 bit bit the plug although it's a hex and pulled it out. It's right behind the exhaust manifold.

Well contrary to what has been posted on this board it is not a 3/8 NPT plug.

It's a 5/8x18 SAE. I have a 3/8 NPT reducing bushing for the sender and it is too large. Just a FYI for one one else looking at this option. I ended up sticking it in the t-stat housing.

That's weird. I have a 3/8 NPT plug in my 99 block, and it fits perfect.

It's actually a special 5/16" square. Snap-On sells one, or you can do like me and grind two sides of a 3/8" extension.

I have to grind down a 3/8" ext. in order to drain and fill the pukegoat.

wait, are we talking about the threads or the drive size? Threads are 3/8 NPT (national plumbing tapered thread), the drive head is 8mm square metric

threads on the plug I pulled out are 5/8". 3/8 NPT is too big to even fit into the hole. The hole location is right behind the exhaust downpipe/header and freeze plug 5 area.

maybe it is 1/4 NPT... I know I used an off-the-shelf brass bung

Adapting 5/8"-18 female hole to 3/8" NPT: http://www.turbowholesale.com/product.php?cat=66&page=2&productid=9584