Standard North American DTIs are made to ASTM F959/959M (metric), which define the chemical, mechanical (read compression load vs. residual DTI gap), and dimensional requirements per ASME B18.2.6. Complete DTI dimensions and mechanical properties are available from ASTM and ASME. Thefollowing is a summary of ASTM F959/F959M.

ElementType 1 SeriesType 3 Series
Carbon0.27 – 0.58
Manganese0.47 – 0.93
Phosphorus, Max0.0480.045
Sulfur, Max0.0530.055
0.13 – 0.37
0.42 – 0.68
0.22 – 0.48
0.22 – 0.48
Product Analysis Chemical Composition Requirements, %

Mechanical Requirements

DTIs are made to compress in proportion to the applied load or bolt tension. A sample of the lot must demonstrate a compression load range at a residual gap of .015” within the following values (the minimum is based on 70% of the minimum ultimate tensile strength of the applicable bolt grade, and the maximum is 20% higher than that). Note the F959/959M stipulates that the compression load test gap of .015” be the same whether the DTI is plain finish or coated. Note that the laboratory certification compression load tests for DTIs DO NOT involve bolts, but rather the tests are performed with the DTIs compressed between hardened mandrels.

Diameter [mm]A325MA490M
M1691 – 109114 – 131
M20142 – 170179 – 206
M22176 – 211221 – 254
M24205 – 246257 – 296
M27267 – 320334 – 384
M30326 – 391408 – 469
M36475 – 570595 – 684
Acceptable Range of Compression Loads (kN) Per ASTM F959/959M Table 2


F959/959M only allows for mechanical galvanizing (to ASTM B695 class 55) and the thermal diffusion process (to ASTM A1059 class 25). Other coatings are allowed with the approval of both the manufacturer and the purchaser. Coating of DTIs by anyone other than the manufacturer is prohibited because ASTM compression testing must be done after coating.

Heat Treatment

Through-hardening to a maximum hardness of HRC37.


ASTM F959/959M requires that compression test certifications be issued which show the results of 29 pieces selected at random from the manufactured lot and compression tested according to Table 2. The compression load of all 29 pieces must be within the range stipulated above. Applied Bolting makes all product material test reports available by download.

DTI Markings

All DTIs are stamped with an individual unique lot mark, which can be related to the lot number. Through the lot number, all DTI lots are traceable to date of manufacture and compression load properties.


DTI shall conform ASME B18.2.6 or ASME B18.2.6M. The number of protrusions may be altered if performance requirements are met. The minimum outside diameter of the DTIs may match the minimum outside diameter of a corresponding ASTM F436/F436M washer.