#20 Diameter Screws

Welcome to the “20-Diameter Screws” collection at Old West Iron. This category organizes our screws by shank (major-thread) diameter — specifically screws sized #20 — not by head size or head style. A #20 screw has a major thread diameter of about 0.320 inches (5/16 inch). 

These #20 screws represent heavy-duty fasteners — thick and strong enough for demanding jobs involving thick wood, large timbers, structural framing, decks, exterior lumber, and other load-bearing or rugged construction where maximum holding power and durability are essential.

FAQ

Q: What does “#20” mean on a screw?
A: “#20” is the gauge size — referring to the diameter of the screw’s threads (outer/major-thread diameter), not the head size or style. 

Q: Why are the screws grouped by shank diameter instead of head size?
A: Because the shank diameter determines a screw’s structural strength, load-bearing capacity, and the size of pilot-holes or clearance holes required. Head size or style affects only appearance or how the screw sits, not its basic gauge or holding strength.

Q: What kinds of projects are #20 screws best suited for?
A: #20 screws are ideal for heavy-duty applications: thick lumber framing, heavy structural assemblies, large timber constructions, decks, barns, heavy furniture, exterior woodwork, or anywhere you need maximum holding strength and reliability.

Q: Will screws under the #20 grouping come with varying head styles?
A: Yes. Because we group by shank diameter only, screws in the #20 collection may have different head types (flat-head, round-head, decorative, etc.). Head design affects appearance or installation method — not the screw’s gauge or strength.

Q: Should I pre-drill pilot holes when using #20 screws?
A: Yes — especially when working with dense or thick lumber. Drilling a pilot hole sized appropriately to the screw’s root (or slightly under its major-thread diameter) helps avoid splitting, ensures clean installation, and maximizes holding strength.