MTJNR 12-3B — toolholder, 0.750" square shank, 4.5" overall length. Made in the USA by RMC Tooling.
3°Side Cutting Edge Angle for Negative Triangle TNM_ Inserts.
Indexable turning toolholder from RMC Tooling, machined in the United States. The shank is ground to a qualified reference surface, so the tool goes back into the turret at the same cutting-point location every time it is swapped — no re-touching off, no lost setup.
Built for production lathes and CNC turning centers. The insert pocket, seat and clamping hardware are all standard RMC service parts, listed below, so the holder stays in service for years instead of being scrapped when a clamp screw strips.
These are the service parts RMC lists for this exact model — not a generic cross-reference. Every one is stocked.
| Insert | TNM_-322 — 3/8" I.C. · 1/8" thick · 1/32" nose radius or TNM_-332 (e.g. TNMA 332) — 3/8" I.C. · 3/16" thick · 1/32" nose radius |
| Seat / shim |
ITSN-333 or ITSN-322 |
| Lock pin | NL-34L |
| Clamp | CL-6 |
| Clamp screw | XNS-36 |
This tool is listed for more than one insert size. The seat has to match the insert you pick — tell us which size you are running and we will pair it for you.
See all RMC spare parts & hardware →
Not sure how to read an insert code? Turning insert designation explained.
Dimensions as published in the RMC 2020 catalog, page 17.
