Reference charts

Engineering reference charts

The tables machinists, engineers and buyers keep open while they design, quote and inspect: threads and fasteners, fits and tolerances, surface finish and hardness, stock sizes and drawing symbols. Values come from the standards formulas where one exists, and each chart says what to confirm against the spec.

24 reference charts, free, no sign-in.

Attach a drawing (PDF or STEP) or describe the part; a U.S. shop that fits quotes it.

Threads and fasteners

  • Tap & drill size chart

    Tap drill sizes for UNC and UNF inch threads at 75% thread, with drill designation, decimal and mm.

  • Unified thread dimensions

    UNC, UNF and UNEF basic major, pitch and minor diameters with tap drills, #0-80 to 1-1/2, in inches and mm.

  • Metric thread dimensions

    ISO metric coarse and fine threads, M1.6 to M48: pitch diameter, minor diameters and tap drill in mm and inches.

  • NPT pipe thread dimensions

    NPT/NPTF 1/16 to 4 NPS: TPI, pipe OD, hand-tight and effective thread length, pitch diameters and tap drills.

  • Clearance hole chart

    Close and free fit drills for #2 to 1 in screws, and ISO 273 fine, medium and coarse holes for M1.6 to M36.

  • Counterbore dimensions

    Socket head cap screw counterbores, inch and metric: head size, counterbore diameter and depth, clearance hole.

  • Countersink dimensions

    82 degree inch and 90 degree ISO 10642 flat head countersinks: head and countersink diameter, tool depth, clearance hole.

  • Dowel pin hole sizes

    Press-fit and slip-fit holes for inch and ISO 8734 dowel pins, with the pin tolerance and resulting fit.

  • Keyway dimensions

    ASME B17.1 and DIN 6885 key and keyseat sizes by shaft diameter, with depth checks across the shaft.

Fits and tolerances

  • ISO 2768 general tolerances

    ISO 2768-1 default linear tolerances by size range and class, the deviations behind an "ISO 2768-m" title block.

  • Preferred fits chart

    ISO 286 preferred hole-basis fits computed for standard sizes: limits, clearance or interference, and what each fit is for.

Surface finish and hardness

  • Surface finish chart

    Surface roughness Ra and N grades in um and uin, with the machining processes that reach each finish.

  • Ra to Rz conversion

    Why Ra and Rz do not convert exactly, and the typical Rz range for each Ra by machining process.

  • Hardness conversion chart

    Steel hardness conversions between Rockwell C, Vickers, Brinell and approximate tensile strength, with a converter.

  • Aluminum temper chart

    What F, O, H and T temper designations mean, from H32 to T651 and T7351, and which alloys use which.

Stock sizes

  • Sheet metal gauge chart

    Gauge to thickness for steel, galvanized, stainless and aluminum in inches and millimeters.

  • Standard sheet sizes

    Common mill and service-center sheet sizes by material, with the thickness range each comes in.

  • Standard plate thickness

    Standard plate thicknesses in inches and mm, common plate sizes, and what is stocked in each material.

  • Standard bar stock sizes

    Round, square, hex and flat bar size increments commonly stocked, by material family.

  • Tube and pipe sizes

    Mechanical and structural tube OD and wall sizes, and how OD-specified tube differs from NPS pipe.

  • Pipe schedule chart

    NPS 1/8 to 24: outside diameter, wall thickness and inside diameter by schedule, inch and mm.

Drawing symbols

  • GD&T symbols

    All 14 GD&T symbols by category, with datum and MMC/LMC rules, the Y14.5 modifiers and how to read a feature control frame.

  • Welding symbols

    How to read AWS A2.4 welding symbols: reference line, arrow and other side, basic and supplementary symbols, dimensions.

  • O-ring sizes and glands

    AS568 O-ring sizes in inches and mm, the five cross-sections, and gland depth, groove width and squeeze by seal type.