I like the round (cylindrical) boring bars in an Aloris style holder. These bars use replaceable HSS toolbit stock. You can easily grind and rotate for any approach you want. I use a small telescoping/swiveling automotive inspection mirror to set it up on the backside threading OUT. This allows me to creep in to an exact depth (I use a long dial indicator for this) to start exactly the same every time and trip the threading lever to GO at the critical part instead of to STOP.
Remember to run the lathe in reverse. I attach a blocking lever to my engagement handle to keep me from inadvertantly starting the chuck the "normal" way. I had one crash, this taught me to block the handle. Cool thing is, you can play with speeds and never have to worry about crashing.
al