Product and application brief
A washer-type direct tension indicator uses raised protrusions that compress as a bolting assembly develops axial tension. Its specified compression response provides an installation indication; it is not an ordinary bearing washer, spring washer or universal anti-loosening device. Select it with the complete fastener and inspection requirements.
Product forms and reference names
| Choice or field | What to identify |
|---|---|
| Conventional protrusion-type DTI | Raised features leave spaces for the specified gap-check method as compression develops. Identify product code, finish and the acceptance procedure; protrusion count is not a universal identity. |
| Product-specific visual indicator | Some proprietary DTIs add an indicating medium or self-indicating feature. Colour, indication pattern and any supplementary gap check follow the chosen product instructions, not a generic rule. |
| Structural bolting DTI | Specify the exact structural bolt grade/type, series and indicator designation under the chosen F959/F959M edition; do not select solely by thread diameter. |
| Cap-screw, anchor or stud DTI | A different DTI specification may govern these assemblies. F2437/F2437M is a separate scope, not a synonym for structural F959/F959M or proof of interchangeability. |
Separate the standard identities and editions
ASTM lists F959/F959M-26 as active for compressible-washer-type DTIs used with structural fasteners. Its published scope relates indicator types to particular structural bolting assemblies and distinguishes inch and metric systems. ASTM separately lists F2437/F2437M-17(2023) as active for carbon/alloy steel DTIs used with cap screws, bolts, anchors and studs. Name the specified edition and designation; these identities do not establish supplied-part conformity.
Compression indication is not a torque reading
TurnaSure explains its DTI structure through compression of protrusions in response to axial force. This distinguishes the indication from a torque-only assumption. The load/compression relationship, initial gap and acceptance criteria must be supported by the chosen product and applicable inspection procedure; this page gives no universal gap, force, accuracy or torque value.
Conventional versus visual inspection
Portland Bolt distinguishes standard DTIs checked with a feeler gauge from its Squirter branded form that releases coloured indicating media. TurnaSure describes a separate self-indicating product. Those are manufacturer-specific structures, not proof that every DTI has a visual signal or that any one colour confirms acceptance. Follow the selected inspection instructions and required records.
Bearing position, turning element and access
Identify where the indicator sits, which head or nut turns, the hardened contact surface and any required bearing washer. Provide access for the specified inspection method. An ordinary flat washer or an arbitrary stack cannot be assumed to preserve the intended compression response; use the approved assembly arrangement rather than inventing a placement rule.
Keep identification and inspection evidence with the lot
Request the applicable product designation, lot identification, finish and compression-test evidence, together with the project verification and inspection instructions. The selected procedure should address assembly verification, installation observations and acceptance records. Do not treat a compressed-looking ring, residual colour or an old used indicator as fresh proof of adequate bolt tension.
Specification fields
| Choice or field | What to identify |
|---|---|
| Indicator identity | Exact product/DTI designation, standard and edition, inch or metric series and controlled drawing or approved product code. |
| Matched assembly | Bolt, nut and bearing-washer grades/types, thread size, grip and hole/recess arrangement; structural, anchor/stud or cap-screw service. |
| Contact and placement | DTI bearing position, protrusion-facing surface, turning element, required hardened interfaces and inspection access; provide the selected assembly drawing. |
| Compression and inspection | Required tension/compression basis, lot verification, selected gauge or visual method, acceptance procedure and inspector records; values must come from controlled requirements. |
| Dimensions and finish | Required bore, outside envelope and pre/post-compression clearance; coating and material designation, compatible surface condition and product instructions. |
| Installation and handling | Approved tightening method, verification equipment, storage/protection and damaged/previously compressed indicator handling; no generic reuse permission. |
| Order and documentation | Quantity, lot segregation/markings, compression test reports, requested conformity documents and project requirements; actual supply/approval/delivery require confirmation. |
Common product questions
Can an ordinary hardened washer replace a DTI?
No automatic replacement is established. A DTI has a specified compressible-protrusion response and inspection function; an ordinary hardened washer is primarily a bearing element.
Does a coloured signal always remove the need for a feeler-gauge check?
No generic rule applies. Visual indication and any supplementary checks depend on the selected proprietary design and the project acceptance procedure.
Can I calculate bolt tension from this reference picture?
No. A generic render has no calibrated compression response, measured gap, lot test or installation context. It cannot establish tension, compliance or safe reuse.
Related product choices
- Hardened washers: bearing elements and structural system selection
- Structural bolts: specify the complete fastener assembly
- Studs and rods: identify the required indicator scope
- Anchor rods: application-specific tension and assembly requirements
Product references
References checked 10 October 2026 identify structures, not FastenerBridge stock, certification or brand affiliation. Final requirements follow the selected specification. No universal dimensions, load rating or tightening torque is stated.