Maybellene,

I bought these for my 1954 3/4 ton.

They will fit your 1957 3/4 ton.

2 & 5/16" O.D.

see PIC @ photobucket

http://i669.photobucket.com/albums/...rontWheelGreaseCapsGMNOS_zps9d411460.jpg

Original part GM # 3680897
Superseded to:GM # 3768604

Chicago auto parts has ( 1 ) GM # 3768604
Phone: 815-614-3122

Friesens Chevrolet has ( 1 ) GM # 3768604
Phone: 402-773-5538

Hope this helps.

George
in
New Jersey

1954 3600
A big help to many on the Bolt
Now cruising in
The Passing Lane