3/8″ Round Boring Tools
Sherline offers boring tools with two different tip shapes: The P/N 2259 boring tool accepts an 80° carbide insert and requires a minimum hole size of 1/2″. P/N 2260 accepts a 55° carbide insert and requires a minimum hole size of 3/4″. 
In addition to fitting into a smaller hole, the 80° holder offers a little more strength, while the 55° holder will cut into a sharper corner. The total length of the tool is 3-1/4″, and with full insertion in the tool post (2 hold-down screws engaged on the flat) you can bore a hole about 2″ deep. Further extension is possible but not recommended due to the potential for tool flex.
Each tool comes with one carbide insert, a hold-down screw of the appropriate length and a T7 Torx key to tighten the hold-down screw. The holders can be held in the round hole of the P/N 7600 tool post for use on a Sherline lathe.
Using a boring bar
The boring bar is designed with a flat on the top surface. The two hold-down screws of the P/N 7600 tool holder are tightened on this flat to both lock the tool in position and keep it from rotating. Extend the tip of the tool only as far as necessary to bore the depth you need. The farther the tool extends from the holder, the more it can flex. This can cause you to bore a taper, give a poor finish or, in extreme cases, cause the insert to dig in or break. The further the tool is extended, the lighter the cut should be. Sherline used to offer a longer boring bar made by another manufacturer, but we now make this one ourselves and have limited the length to what we feel is safe and appropriate for Sherline tools. If you have a longer bar we do not recommend you extend the tool more than a few inches from the holder to limit tool flex.