Fastener & Thread Reference

The NPT (National Pipe Taper) reference: threads per inch, actual pipe outside diameter, and the typical tap drill for each nominal size from 1/8" to 4". Note that NPT sizes are named by nominal bore, not the measured thread diameter.

The metric fastener numbers you look up at the machine: coarse-thread pitch, tap drill (~75% thread), normal clearance hole, and socket cap-screw hex key for M2 through M20 — one spec sheet per size.

A searchable thread, drill, and tap tool covering both systems in one place: Unified inch (UNC/UNF) and metric (coarse and fine). Look up thread pitch or TPI, major diameter, the tap drill for a ~75% thread, and a clearance-hole size where a reliable standard exists. Search by size (e.g. 1/4, M6) or filter by system and series.

The across-flats wrench (spanner/socket) size for standard hex-head bolts and nuts, metric and inch in one searchable chart. Search a fastener size (e.g. M10, 1/2) or filter by system. Across-flats is the flat-to-flat hex dimension — the size stamped on the wrench.

The correct tap drill sizes for Unified inch threads (UNC coarse and UNF fine) at ~75% thread engagement — the shop-standard chart, with drill number/letter/fraction and decimal size for each screw size.

Pick the right threadlocker by strength, thread size, temperature, and whether you need to remove the fastener later — a quick comparison of the common Loctite grades (purple 222, blue 242/243, red 262/271/272, green 290 wicking) with color, strength, size range, and removal.

Decimal-inch and millimetre equivalents for the standard drill series — fractional (by 64ths), number (#1–#40), and letter (A–Z) — so you can convert any drill callout to a size you can measure or order.

Standard thread pitches for metric (ISO) coarse and fine threads in millimetres, and Unified inch (UNC/UNF) threads in threads-per-inch — with how to use a thread pitch gauge to identify an unknown thread.

Find how many threads are engaged over a length and the engagement-to-diameter ratio, with typical minimum engagement by mating material so the tapped thread isn't the weak link.

Calculate the cutter depth to open a countersink to a target diameter at 82° (inch flat head) or 90° (metric) — so a flat-head screw sits flush.

Standard head diameter, head height, and hex key size for inch (ASME B18.3) and metric (ISO 4762) socket head cap screws — the numbers you need to size counterbores and clearance holes.

Pick a socket head cap screw and get its head dimensions plus a recommended counterbore diameter and minimum depth so the head seats below flush — inch or metric.

Standard metric clearance holes (ISO 273) for a bolt through a part — close, normal, and loose fits — so the fastener passes through without binding.