Dating Vise Grip design changes .

[Mr_B]

Any one know what year the cross lever changed from design in pic 1 to design like still in use today in pick 2
any other design change dates be cool info too, (such as patent number on lower handle to vise grip registered trade mark stamping)
I picked up a nice clean pair of 7R grips this morning at a yard sale and it got cross lever like pic 1 and got me wondering how old they are and actual date manufacture changed .

pic1


pic2

 

[Mick56]

A couple bits of info I have are:
The logo moved from the side of the fixed jaw to the handle around 1947.
The model number was put on the movable jaw about 1950.
The release lever was added around 1957.