Lag screws

Stud Bolt – Overview
A stud bolt is a headless fastener threaded at both ends, used in applications that require precise preload, often in machinery, equipment, and flange connections. One end is permanently threaded into a tapped hole, while the other end remains free for nut fastening.

DIN Standards and Dimensions
DIN 938 – Stud bolt
One end shorter (n1) = 1x the screw diameter, the other end longer (n2)
Plain shank length in the middle
Effective length = total length - n1
Applications: machines, cylinder heads, gearboxes
DIN 939 – Stud bolt
One end shorter (n1) = 1.5 x the screw diameter, the other end longer (n2)
Applications: general joints where symmetry is required
Partially replaced by ISO 898-1 and ISO 225, but still widely used

DIN standards define:
Lengths of threaded sections
Thread tolerances
Surface finish and length dimensions in class A or B

Uses of Stud Bolts
Typical applications:
Engines (e.g. cylinder heads)
Piping and flanges
Pressure vessels and couplings
Heavy machinery and gearboxes
Advantages:
The bolt does not back out of its thread during use
Better control of clamping force
Replaceability (the nut can be removed without damaging the threaded hole)
Suitable for repeated opening and closing

Materials
Material - Application - Notes
8.8 or 10.9 high-strength steel - General machining and equipment construction - High tensile strength
A2-70 (stainless steel) - Outdoor use, chemical environments - Corrosion resistant
A4-80 (acid-resistant stainless steel) - Seawater, food, pharmaceutical industry - Highly corrosion resistant
Brass - Light-duty joints, electrical installations - Non-magnetic, good electrical conductivity, not a stock item

Installation Notes
Always use the correct grade of nut and washer for compatibility
A threadlocker can be used on the fastening end (e.g. anaerobic adhesive)
Torque tightening is important to achieve the correct preload