I have one of the Shars internal threading boring bars pictured below. Runs around $38 + shipping, includes 1 insert - model # 404-2290. Style is 16 IR A60 or 16 IR AG60. Hit eBay for more inserts instead of Shars, you can get them for under $3. There's a picture below of it threading a piece of stainless.
By the way, make sure if you buy one of these bars you get the right sized inserts. 3/8" inserts are 16 series, 1/4" inserts are 11 series. The lettering after 16 or 11 should be IR for internal RH threads (E for external, L for left-hand threads). An AG60 insert is good for threads from 8-48 tpi, A60 is 16-48 and G60 is 8-14 tpi. They also sell them with UN suffixes; number in front is for that specific tpi. For example, 16 IR 14 UN is a 3/8 internal RH thread 14 tpi. 11 IR AG60 is 1/4" internal RH 8-48 tpi insert.
Bruce
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