Identify screw threads from measurements — free online thread identifier for metric, UNC, UNF, BSP, NPT, ACME and 11 other thread standards.

Units
Thread Type
Major Diameter (mm)
mm
Pitch (mm)
mm
Threads per Inch (TPI)
TPI
Tolerance ±5%
  1. 1
    Select units

    Choose mm or Inch depending on how you are measuring.

  2. 2
    Select thread type

    Use External for bolts/studs, Internal for nuts/tapped holes.

  3. 3
    Measure the diameter

    For external threads, measure the outer (major) diameter with calipers. For internal threads, measure the minor (inner) diameter of the bore.

  4. 4
    Measure the pitch or TPI

    Use a thread pitch gauge or count the number of thread crests over 25.4 mm (1 inch) to find TPI. Alternatively enter the pitch directly in mm or inches.

  5. 5
    Tap Identify Thread

    Results are ranked by match quality. Excellent Good Acceptable Poor

About This Thread Identifier Tool

ThreadChaser is a free online tool to identify screw threads from measurements. Measure your bolt, screw, or threaded hole with calipers or a thread pitch gauge, enter the dimensions, and the tool instantly identifies the matching thread standard from a database of over 300 thread sizes. It is the fastest way to identify a thread from measurements without needing a full set of thread gauges.

Supported thread standards include Metric Coarse (ISO 724), Metric Fine, UNC (Unified National Coarse), UNF (Unified National Fine), UNEF (Unified Extra Fine), BSP (British Standard Pipe), BSW (Whitworth), BSF (British Standard Fine), BA (British Association), NPT (National Pipe Taper), ANC, ANF, ACME, Buttress, Square, and Knuckle (DIN 405).

Use it to identify external threads on bolts and studs, or internal threads in nuts and tapped holes. Works in millimetres, inches, and TPI (threads per inch). Results are ranked by match quality with full dimensional data including major diameter, pitch diameter, minor diameter, pitch, and tapping drill size.

Reference aid only. Always verify critical dimensions directly against the relevant published standard, and use calibrated measurement instruments. Do not solely rely on this website where incorrect thread identification could cause injury, death, or property damage.