IRD QB55 - Square Taper Bottom Bracket
The Shimano bottom brackets are fine but these are an upgrade without going all the way up to Phil Wood. They're made in Japan by Tange and will last a long time.
If you're using a Silver crank with a "MTN" front derailler, get a 113. If you're using a road front derailler: 110mm. If you're squeezing a big tire onto a Clem and want a little more chain clearance in the low gears, get a 118; It'll work perfectly.
If you have a GUS or SUSIE hillibike with a tire up to 2.5-inches, you'll need a 123 with the right-cup spacer. Wider than that, get the 127. Be prepared to struggle finding a front derailer that'll shift out that far, but if you're doing a double and the big ring is inside the spider, no problem. Keep in mind, tho, brothers and sisters--you're basically paddling your canoe across Yosemite Creek just before it turns into Yosemite Falls. It's not conservative, and unanticipatable frustrations are part of the game...when you do that.
for 68mm shells. JIS taper, BSA threading.