Flea market find, and what does HSG stand for

[JimDawson]

The 2 end mills that have HSG, and HSG8 also have the brand name Union on them.

I did a pretty extensive web search on UNION BUTTERFIELD HSG and found reference to both HSG and HSG8, and the best I can come up with is that it may be part of an old part numbering system, probably designating the grade of the HS steel.

 

[markknx]

Thanks Jim that's kind of what I was wondering if it was a certain kind of HSS, maybe a cobolt or some thing. Thanks to all that chimed in here with helpful info. Mark