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Double Thread Lag Screws

Double Thread Lag Screws

Double Thread Lag Screws

Double thread lag screws (also called hanger bolts) have a machine thread one end and a wood thread the other. The wood thread screws into the timber substrate; the machine thread projects out for nut-and-bolt hardware attachment on the other side. Used to mount machine-threaded fittings into timber where a through-bolt isn't possible.

Also known as: Hanger Bolt, Stud Bolt, Double End Lag Screw, Machine and Wood Thread Bolt.

Stainless A4-70 G316 double thread lag screws in M8 x 100mm and M10 x 60-100mm. The machine-thread end is approximately 30-40mm; the wood-thread end is the balance of the screw length.

GRADES AND MATERIALS

Stainless A4-70 G316 (marine grade): 700 MPa minimum tensile, 316-family austenitic stainless with added molybdenum (2-3%) for chloride-pitting resistance. The standard for direct saltwater exposure, ocean spray, chlorinated pool plant and food-grade processing. Largely non-magnetic - cold-formed sections may show slight residual magnetism from manufacture.

INSTALLATION AND USE

Drill a pilot hole in the timber matching the wood-thread minor diameter (M8 = 5-5.5mm, M10 = 6.5-7mm). Drive the wood-thread end into the timber by locking two nuts on the machine-thread end and turning the nut pair with a spanner. Stop driving when the wood-machine transition reaches the timber face. Remove the two nuts; the machine thread is now ready for fitment hardware.

A NOTE ON GALLING

Stainless threads can gall under tension - apply a thin film of nickel-based anti-seize from the Anti-Seize range to the male thread before assembly. Tighten slowly, never with an impact driver.

SIZE AND WLL

WLL is set by the lower of the wood-thread pull-out strength and the machine-thread shear strength. M8 in pine = ~250kg pull-out; M10 = ~400kg. Hardwood 1.5-2x; end-grain 50% of side-grain.

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