There is a pair of round nuts on the outside diameter of the axle tube with a sheet metal lock ring in between them. They have a series of notches on the face of them that a special 'hub wrench' fits into.

The lock ring will have one or more tabs bent over into the notches on the face of the outer nut to lock it in place. Pry the tabs out of the notch and up against the inner diameter of the hub to 'unlock' the outer nut.

Most people just use a hammer and a good sized punch to tap on the sides of the notches and turn the nut in lieu of the special tool.

I discovered a few years ago that the special nuts and lock rings to fit my '38 1-1/2 ton year end are still available from GM. They're listed for a late 90's 1-ton rear axle and are exactly the same as the '38 parts. I have the numbers if anyone is interested.

'38 Chevy 1-1/2 ton
'49 Chevy 1/2 ton
'54 Chevy 6400 2 ton
'55.2 GMC 3/4 ton
'56 GMC 1-ton

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