Small-bore boring is where indexable tooling runs out of room. Below about half an inch there is no space to seat an insert and a screw, so the bar has to be ground from one piece — and in a bore that small, the bar is thin enough that its stiffness decides the result more than anything else in the setup. Solid carbide is roughly three times as rigid as steel, which is why these exist.
What that rigidity buys is a bore that stays round and on size down its full depth instead of belling out at the mouth, and a finish that does not carry the chatter pattern a deflecting bar leaves behind.
What is in this range
Minimum bore: .090" through .360"
Shank diameters: 1/8", 3/16", 1/4", 5/16" and 3/8"
Material: solid carbide, ground
Origin: made in the USA by HTC Mfg.
Two habits pay off with any small boring bar: keep the overhang to the shortest length that reaches the bottom of the bore, and take the finishing pass light, because a thin bar deflects under load and a light cut deflects less.
