When a plastic-molding buyer orders brass insert nuts with knurling, the failure mode is almost always the same. The knurl pattern bites unevenly into the resin, or a thread-gauge check at receiving reveals a half-pitch mismatch. The part looks right on the drawing. It is not, and the tooling cycle is already paid for.
What brass material fits knurled inserts
For most plastic-molding and sensor-housing applications, C36000 free-machining brass is the default. It cuts clean through the knurling operation and holds a uniform dimple pattern on the outer surface. If the part sits in a salt-spray or marine environment, spec C26000 naval brass or a 316 stainless body with a brass thread.
That one material call shifts your quote by 15 to 30 percent. Weeda Precision works from your drawing for both standard brass and stainless variants, so the material swap is a pricing conversation, not a redesign. Confirm the alloy and the finish—bright, satin, or coated—before you lock the BOM.
How tight a tolerance on knurled inserts
The knurl depth on a 1/4-20 insert typically runs 0.004 to 0.006 in. A 0.002 shift in OD tolerance changes the whole grip. Call out the pattern—straight or diamond—the depth, and the smooth-shank length before the knurl zone. Skip that detail and the shop runs a generic pattern you discover at the molding trial.
A knurled OD is difficult to measure with a mic. Ask for a thread-gauge report (GO/NO-GO) plus a surface-finish reading on the smooth section. Weeda Precision includes a first-article inspection report with each prototype batch of these precision turned parts, so you are not waiting on a separate CMM session to clear incoming stock.
What RFQ needs for knurled inserts
Prototype runs of 50 to 200 pieces let you verify the knurl bite on your specific resin before committing to volume. Once annual volume exceeds 10,000 units, a dedicated knurl die pays off and lead time drops from five weeks to two or three. Pack in individual plastic dividers; loose bagging scratches the knurl face and voids the finish spec.
Include the drawing revision number, the exact thread class (2A or 2B), total length with a dimensioned break between smooth and knurled zones, and your annual volume. State the resin type and the molding cycle temperature. That trims one round of Q&A and keeps the build schedule on track.
Before you release the RFQ, pull one last molded assembly and check thread engagement under a 10x loupe. That fifteen-minute check at your own bench saves a whole batch of rework downstream.