manual box fill plug?

[Badvert65]

I have a 1965 Belvedere I with manual steering. I was cleaning the dang fill plug for it with the wire wheel side of my bench grinder. Well, it got 'loose' and the grinder flung it somewhere, possibly another dimension as I am unable to find it.
Does anyone know what size plug it is? I measure the hole and it seems to be 24 thread, around 5/8 inch, but....I can't find anything like that in searches.
Anyone know the size or a source for this dang thing?
-Matt

 

[moparmarks]

Should be 1/2" NPT.

 

[R/T Boy 67]

Your best bet would be to find your plug. 5/8 -24 is an extra fine series of thread, probably not common. It is not a NPT with 24 TPI.

 

[moparmarks]

Man, talk about having a major brain fart. He wrote manual steering and my brain saw manual transmission.
Never mind.

 

[R/T Boy 67]

Brain fart, is my middle name.