Bit shanks (Myler bits)--flat versus HBT?
I'm trying to buy a new (western) bit. I know which mouthpiece I want, but I don't know which shanks style.
The one I want is a Myler, with 5 inch shanks, but they offer several shank options with the mouthpiece I want. Myler offers a flat shank and an HBT shank. I don't know what HBT stands for, maybe that would help, but I couldn't seem to dig that up.
So essentially my questions are: what is Myler's HBT shank? Visually, it is round as opposed to flat, but what is the difference in function between this and a flat shank?
Any insight would be greatly appreciated. Thanks!
PHOTOS:
Flat shank:
http://www.rods.com/pl/ShowBook06,11025_L,799,4996_Myler-Comfort-Mouth-Mullen-Barrel-Bit-by-Toklat.html
HBT shank:
http://www.rods.com/pl/ShowBook06,89-20015_L,799,5002_Myler-HBT-Comfort-Mouth-Mullen-Barrel-Bit-by-Toklat.html
Hopefully that helps.
Multiple shank lengths are available on both types.