How to Measure a Flat / Countersunk Screw
A flat-head countersunk screw is a key exception: its nominal length includes the head.
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TOP VIEW
82 deg
QUICK RULE
A flat-head countersunk screw is a key exception: its
nominal length includes the head.
LENGTH
Length includes the head - measure from the top
LENGTH: top plane of the flat/countersunk head -> end of fastener.
Do NOT start at the underside of the head as you would on a hex cap screw.
Measure nominal diameter and thread independently.
Countersink angle/head dimensions are product-standard dimensions; verify the applicable
standard.
This rule applies because the flat head seats into the work and becomes part of the
installed length.
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-54F2A4 · thefastenerapp.com/fastener-guide/measure-and-identify/how-to-measure-a-flat-countersunk-screw · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
