Fastener Guide / Technical Reference

ASTM F959 Direct Tension Indicator Washers

Direct tension indicators (DTIs) are washers with bumps that flatten as the bolt reaches its required tension. A feeler gauge check confirms installation.

Last reviewed 2026-09-10 · Governing standard: ASTM F959/F959M-17a (R2023); RCSC Specification · reference FG-CA1E44 · Report an error on this sheet

DTI types

TypeUse with
325 (and 325-3 weathering)A325 / F1852
490 (and 490-3 weathering)A490 / F2280

These tables carry the same figures as the printed sheet below.

The printed sheet

ASTM F959 Direct Tension Indicator Washers

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Text version of this sheet

ASTM F959 · direct tension indicator washers

FIELD IDENTIFICATION

What it is

Direct tension indicators (DTIs) are washers with bumps that flatten as the bolt reaches its required

tension. A feeler gauge check confirms installation.

Bumps flatten as the bolt reaches tension

DTI types

Type

Use with

325 (and 325-3 weathering)

A325 / F1852

490 (and 490-3 weathering)

A490 / F2280

Key points

325 and 490 DTIs are not interchangeable.

Usually placed under the bolt head with bumps facing the head; follow the manufacturer and RCSC.

Governing standards: ASTM F959/F959M-17a (R2023); RCSC Specification. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard

always take precedence over this sheet.

torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability

arising from reliance on this reference.

Fastener Guide reference FG-CA1E44 · thefastenerapp.com/fastener-guide/technical-reference/astm-f959-direct-tension-indicator-washers · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.

Related sheets

← ASTM F844 / USS / SAE Flat WashersASTM A320 Low-Temperature Bolting →

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