UNC. UNF. Metric. Pipe. ACME.

UNC (Unified Coarse) has fewer threads per inch — easier to start, less prone to cross-threading, faster to assemble, more forgiving to contamination. Use for: general fasteners, thick materials, field assembly, outdoor use. UNF (Unified Fine) has more threads per inch — higher tensile strength, better for thin materials, better vibration resistance. Use for: precision adjustment, aerospace, high-strength aluminum, thin-wall applications.

Same trade-off as UNC/UNF. Metric coarse (default): M10 × 1.5 pitch, used for 90% of general applications. Metric fine: M10 × 1.25 pitch, for precision adjustment, aerospace, thin-wall. Note: metric threads always specified with pitch (M10×1.5 vs M10×1.25), while inch threads use threads-per-inch (1/2-13 vs 1/2-20). Don't mix up pitch and threads per inch.

NPT (US tapered pipe thread): sealing against tapered mating threads. Requires thread sealant or PTFE tape. Standard for US plumbing, industrial fittings. BSP (British Standard Pipe) comes in tapered (BSPT, like NPT but different taper) and parallel (BSPP/G, requires gasket or O-ring). Common in UK, EU, industrial applications. JIS (Japanese) similar to BSP. For hydraulic fittings, consider SAE O-ring boss instead of pipe thread — better sealing.

Class 2A/2B (external/internal) is default for 90% of threads — standard assembly fit. Class 3A/3B: tighter fit for precision applications, aerospace, vibration-prone assemblies. Class 1A/1B: loose fit, dirt-tolerant, agricultural. Metric equivalents: 6H (default internal), 6g (default external), 4H/4h (tight), 7H/7g (loose). Match class to assembly requirements.

Yes — ACME power threads for linear actuators, Stub ACME, buttress threads, trapezoidal (TR) metric threads, custom square threads. Single-point lathe threading for special pitches not available in standard taps. For very small or unusual threads, thread milling with CNC is often the best approach. Specify pitch, major diameter, minor diameter, and any special thread form requirements.

Standard threads (tap or thread-mill): Class 2B/6H typical, acceptable for production use. Precision threads (single-point lathe threading): Class 3B/4H with go/no-go gauge verification. Thread pitch diameter measurement with thread micrometer or 3-wire method. For aerospace or safety-critical threads, per-part inspection available with calibrated gauges. Rolled threads (for production volumes) typically best accuracy but require specific material and equipment.