FF-B-561 — Lag Bolts (Screw)

FF-B-561 covered lag bolts (also called lag screws) with square or hex heads, used for fastening into wood and similar materials. Its final Revision D, Notice 1 (3 August 1993), was superseded by the commercial standards ASME/ANSI B18.2.1 and ASME/ANSI B18.18.1M, which govern lag screw dimensions and quality assurance today.

Status: Superseded — see ASME B18.2.1 Type: Lag Bolt / Lag Screw Head Styles: Square, Hex FSC Class: 5306

At a Glance

Full Title

Bolts, (Screw), Lag

Superseded By

ASME/ANSI B18.2.1 & B18.18.1M

Final Revision

D, Notice 1, 3 Aug 1993

Head Styles

Square Head, Hex Head

Typical Use

Fastening into wood/timber structures

FSC Class

5306

Prior Revision

C, 1 Dec 1970

Current Guidance

Specify ASME B18.2.1 for new designs

Overview

FF-B-561 covered lag bolts — heavy-duty externally threaded fasteners with square or hex heads and a gimlet or cone point, driven by torquing the head rather than a nut, and used primarily for fastening into wood, timber, or similar materials where a pre-drilled pilot hole receives the coarse lag thread.

Like many hardware-focused federal specifications, FF-B-561 was eventually phased out in favor of the equivalent commercial/industry consensus standards maintained by ASME. The final government revision, Notice 1 to Revision D, points buyers to ASME/ANSI B18.2.1 (Square and Hex Bolts and Screws) and ASME/ANSI B18.18.1M (Quality Assurance for General Purpose Fasteners) as the superseding documents.

FF-B-561 part numbers and NSNs still appear on older engineering drawings and government stock records, even though procurement now references the ASME standards directly.

!

FF-B-561 is superseded. Current and future procurement of lag bolts/screws should reference ASME/ANSI B18.2.1 for dimensions and ASME/ANSI B18.18.1M for quality assurance requirements. This page is retained for legacy drawing cross-reference only.

FF-B-561 — Frequently Asked Questions

What's a lag bolt used for?

Lag bolts (lag screws) are heavy-duty fasteners driven into a pre-drilled pilot hole in wood or similar material, torqued by their square or hex head rather than tightened with a separate nut — commonly used in framing, decking, and heavy timber connections.

Where do I find current lag bolt dimensional standards?

ASME/ANSI B18.2.1 covers square and hex bolt/screw dimensions including lag screws, and ASME/ANSI B18.18.1M covers the quality assurance requirements that replaced FF-B-561's inspection provisions.

Need Lag Bolts to Current Standards?

Ananka Fasteners manufactures lag bolts to ASME/ANSI B18.2.1 with full material traceability.

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