What's new
What's new

Alternative inserts for my 16 IR indexable toolholder


Jul 7, 2010
Northern California
I would like to identify a suitable boring insert for my 16 IR internal indexable tool holder.
I have a Shars 404-2291 internal indexable tool holder, but I do not have an insert for boring the ID to size before I begin using the threading insert.
The Threading Insert is a 16 IR, and Shars claims that no other insert will fit.

My generic el-cheapo Harbor Freight triangular inserts appear to fit, naturally they are devoid of any identifying markings and are dull as rocks.

I'd like to acquire a few triangular inserts I could use for boring mild steel. I am not looking for donations, I'm seeking information about alternative inserts that would fit this tool holder.

What I know:
16 IR: .146" thick 3/8" inscribed circle, or in metric: IC=9.52 INSL=16.49

What I don't know: Which standard triangular insert should I be looking for?
Using the chart at http://www.carbidedepot.com/formulas-insert-d.htm
Theory: TNMG332 ??
N-Zero degree clearance ?
M-Tolerance ?
G-ChipBreaker yes double sided cylindrical
3-Inscribed circle size 3/8
3-Thickness .187
2-Radius .031

More details: I'll be boring 5/8ths inch steel plate 2.2" inside diameter, on a 12" Atlas lathe. I do not have a HSS boring bar.
Last edited:


Oct 14, 2010
Oregon, USA
16IR is an industry standard size. I suppose Shar's "16IR" might not be the same as everybody else's, but you can probably buy suitable inserts from any of the usual industrial suppliers. Travers, KBC Tools, McMaster-Carr, MSC (shudder), or whatever your favorite place to be machine tooling is.

BUT, 16IR (or 16ER for external) is for threading tools, not boring tools. And yes, the folks at Shar's are correct, you cannot buy inserts intended for boring and mount them in your 16IR bar. Nobody makes them. Get yourself a suitable boring bar (and inserts that fit it) to supplement your internal threading bar.

For small diameter boring bars, I like CCMT32.52 inserts (or CCMT21.52 for even smaller boring bars). But there are a skillion reasonable choices. First choose the minimum bore size you need to work with. Then decide what lead angle you need. Then decide if you need a bar that will work steel or if you are only going to be boring aluminum. From those decisions, you can narrow down the choices of 1) insert size, 2) insert shape, 3) insert relief angle, 4) choice of boring bar to hold those inserts at the desired lead angle. I usually use SCLCR boring bars with my small CCMT inserts. But if you prefer triangles or narrow diamonds and a different bar style, that's fine too.
Last edited: