A way of installing high-strength structural bolts that relies on rotation rather than torque. The joint is first brought to snug tight, a match line is marked across nut, bolt end and steel, then each nut is turned a set amount, typically one-third turn for bolts up to four diameters long, one-half for four to eight and two-thirds for eight to twelve. Because the rotation stretches the bolt into its inelastic range, the result is far less sensitive to friction than torque control.
Snug the whole connection first, then paint your match marks, then a half turn on every nut and leave the marks for the inspector.
The painted match marks are the inspector's whole evidence trail, so mark before turning, never after.
Also heard as
- part-turn method
- turn of the nut
Related terms
Snug tight
The first stage of bolting, where the joint plies are pulled into firm contact before final tightening.
A325
The workhorse high-strength structural bolt: heavy hex, quenched and tempered, 120 ksi minimum tensile.
Torque-to-yield
Tightening by torque plus angle until the bolt just yields, giving consistent high preload; the bolt is single-use.
DTI
Direct tension indicator: a hardened washer with bumps that flatten when the bolt reaches required tension.