Master - How to Measure & Identify Fasteners
A practical counter and field guide to identifying unknown fasteners correctly.

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QUICK RULE
A practical counter and field guide to identifying
unknown fasteners correctly.
HEX / PROTRUDING HEAD
FLAT / COUNTERSUNK
under the head to the end
top of head to the end
Start with product type: bolt, screw, rivet, nut, washer, stud or specialty fastener.
Measure nominal diameter across the shank/body - not across the threads with a ruler if a
gauge or caliper is available.
Determine thread: inch diameter + TPI (UNC/UNF) or metric diameter x pitch.
Measure length from the correct datum. Most protruding-head screws/bolts: under the bearing
surface to the tip. Flat/countersunk heads: top of head to tip.
Record head/drive style, material/finish and grade/property-class marking.
Use a bolt/thread gauge as an identification aid; final product callout must match the
governing standard/OEM drawing.
IDENTIFICATION ORDER
Product -> diameter -> thread -> length -> head/drive -> grade/material -> finish -> governing specification
REFERENCE ONLY. Verify the current ASME/SAE/ASTM/ISO/OEM standard and manufacturer data. Do not use as the sole basis for critical fastener selection or installation.
Fastener Guide reference FG-DF6902 · thefastenerapp.com/fastener-guide/measure-and-identify/master-how-to-measure-and-identify-fasteners · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.

























