Internal threads. Any size, any material. Tap or thread mill.

Tapping advantages: much faster (seconds per hole), cheaper tool, standard sizes readily available. Thread milling advantages: better tolerance control, works in hardened materials, single tool handles multiple sizes, no breakage risk in blind holes. For production of standard threads in soft-to-medium materials: tap. For precision threads, hardened materials, or blind holes where tap breakage would ruin the part: thread mill. Thread milling is the "safer" choice; tapping is the "faster" choice.

Three scenarios. (1) Soft materials (aluminum, plastic) under high fastener load — tapped threads may strip; heli-coils distribute load better. (2) High-cycle applications — threads installed/removed repeatedly (panels, service covers); tapped threads wear out. (3) Repair of damaged threads — oversized tap and heli-coil restore functional threads. Cost: $2–5 per installed insert. Plan hole size to accommodate insert diameter.

Classic problem. Tap broken in blind hole is very difficult to remove — often scrapping the part. Mitigations: (1) Use spiral-point taps (push chips forward out of hole). (2) Reduce hole depth to leave clearance below threads. (3) Use thread milling instead — no breakage risk. For critical blind-hole parts, we often specify thread milling automatically to avoid tap breakage incidents.

Standard 75% thread engagement. Example: M6 × 1.0 thread needs 5.0 mm tap drill. Reduced engagement (60%) allows larger drill (5.1 mm) for softer materials, easier tapping. Higher engagement (85%) for strength-critical in hard materials. We specify appropriate drill size based on material and application. See our thread standards guide for complete tap drill chart.

On CNC: tapping integrates into machining cycle. Adds ~2–5 seconds per tapped hole. Cost: essentially negligible on per-part basis for production. For rush or small-batch, tapping can be done on drill press after CNC — slightly more expensive but keeps CNC time focused on primary machining. Thread milling costs slightly more (longer cycle time) but eliminates tap breakage risk and produces better threads.

Standard tapping: no meaningful lead time impact — integrated with CNC production. Specialty threads (non-standard sizes, custom threads): may require custom tooling with 1–2 week lead time. Heli-coil installation: adds 1–2 days to lead time for inserts sourcing and installation. For urgent orders with custom threads, verify feasibility before PO.