Key way broach designations...

[QSIMDO]

Looking to buy my very first key way broach, (awwww...) bushing and shims but there appears to be differences I'm not
familiar.
A cruise through eBay shows designations like " II ' and " III ' and " C ", etc.

Anyone care to explain the differences, I would be most appreciative?

[Highpower]

Spend some time looking through the "bushings, shims" and "resource center" tabs here. http://dumont.com/resource-center/

This will give you a good run down as well. https://www.mcmaster.com/#broaches/=17sv8uc

[tlfamm]

Here's one clue to the letter designations:

"duMONT Minute Man® Keyway Broaches and Bushings have letter designations signifying the body width of the Keyway Broach and the guide slot in the Bushing. The Bushing size and Style are determined by the bore diameter of the workpiece as well as the Style of Broach to be used. “A” Style Broaches are used with “A” Style Bushings, “B” Style Broaches with “B” Style Bushings, etc. duMONT Collared Bushings are “A”, “B”, and “C” Style while “D” and “E” Style Bushings are Plain. “F” Style Bushings are Plain and though considered Special are often available from stock."


http://dumont.com/bushings-shims-pre...roach-style/a/


More info in this PM thread:

http://www.practicalmachinist.com/vb...lature-253783/

[QSIMDO]

Looks as if it determines size mostly, each covering a defined range.

[Highpower]

Yes, basically bore diameter and bushing style mostly as tlfamm pointed out above. The good news is that you can make your own bushings pretty easily if you need an odd ball size, or even a standard size if you don't happen to have one on hand and need one quickly without having to order it.

[Cuttings]

I recently needed a 4mm broach but could not find one locally so bought a 5/32 which is only .001" smaller and the key was on a Chinese made machine so probably was not that close anyway. The broach was a B width which is 3/16". I needed to use this in an 12mm bore so ordered a 12mm bushing with a B designation. I could have made the bushing but was not sure what the slot depth should be. When the bushing came it was a 12mm-B-1 and the slot was 1/4" wide. I ended up making a bushing after all and sent the B-1 bushing back. According to the supplier you can't get a metric bushing with a B slot just the B-1 slot even though there catalogue said it would be B. Kind of confusing. I got the key way I wanted in the end.