A number of years ago, before Sherline started offering tool bits to hold inserts. I bought a set of 3 tool bits from Plastool Plastool
They use the cheapest in cost insert TNMG-222 since that style seems to be the most popular. I just bought 15 of the for under $15.00. The tool bits had a funny looking .05 Cap screw head, not really a button head and not a standard head. At the NAMES show I recently bought the QC tool post set up with two 3/8 tool bit holders. I had always been concerned about dropping/loosing the screws.
I contacted the new owners of the company, as the ME that designed and made them has gone on to the large shop in the sky!
They got back to me with some info. The screws are standard 2-56 button heads, what he did say is that they grind the heads down to a smaller dia for a better look.
I went out and bought a bunch of the screws, so Now I don't have to be concerned about the funny looking heads on the insert hold down screws.
They have other sized insert tool bits. in addition to the Sherline, Taig, Unimat,Prazi
They work well, and a economical alternative if you don't have a carbide sharpening set up.