Mack wrench

[jimwrench]

 Got a Williams( 79S) S wrench today in a box of old wrenchs from a garage sale on a farm. Guess(tongue in cheeK) he once owned a Mack tractor as wrench is so marked. A nice surprize among the rust.

[bonneyman]

Why the S shape? Is it some sort of obstruction wrench?
For a job where a straight won't work, and neither will a half-moon?

[Wrenchmensch]

Jimwrench,

There are more Williams Mack wrenches out there.  A caveat:  Some Williams S-wrenches made for Mack Truck failed. As an example, my large 83A wrench below has 2 cracks at the base of the 5/8 S.A.E. opening.  It appears that wrenches stronger than the Williams S-wrenches came on the market, and a lot of the Williams wrenches were either melted down, or taken home.

[rusty]

>Why the S shape? Is it some sort of obstruction wrench?

Yes and no, the s-wrenches came before the moon wrenches, but I suppose you have to say the straight wrenches came before the s-wrenches if you count cast ag wrenches.

The S-wrench is supposed to be called a 'car wrench', not for car as in automobile, but as in railroad car, which is what they were made for originally. Bolts on rail cars do in fact have lots of obstructions, so it's a good shape for that. Auto mechanics used them more or less because they were already available, but the straight wrenches seem to have replaced them rather quickly at the dawn of the auto age....(It is likely they were also cheaper to forge, due to the simpler shape)

>Some Williams S-wrenches made for Mack Truck failed

Many Williams, and other companies s-wrenches failed, the metal was plain carbon steel, and the head designs were often horribly flawed, for example using back cuts with notches at the peak stress points, virtually guaranteeing fatigue failure would occur.