3/8" Thick 4.125" OD Round Aluminum Tapped Pad | 5/16"-18 UNC Thread | Marine Grade 6061-T6

4.125" OD Round Aluminum Tapped Pad — 5/16"-18 UNC Thread Precision CNC-machined 6061-T6 aluminum round tapped pad with a single 5/16"-18 UNC threaded hole. Designed to receive a threaded fastener directly — no nut required on the back side. Commonly used where a threaded mounting point is needed on a fiberglass deck surface, radar arch, or T-top assembly in saltwater marine environments. Material Marine Grade 6061-T6 Aluminum Outside Diameter 4.125" (105 mm) Thickness 3/8" (0.375") Threaded Hole 1 (5/16"-18 UNC tapped) Shape Round Finish Matte — tumbled, deburred, paint/powder coat ready Weight 0.56 lb Common Applications T-tops, tuna towers, hard tops, radar arches, leaning posts, grab bars, bow rails, outrigger mounts, rod holders — anywhere a threaded mounting point is needed on a fiberglass or aluminum surface. Frequently Asked Questions What is a tapped pad? A tapped pad has internal threads cut into its hole so a fastener screws directly into the pad — no nut or backing plate required on the opposite side. This makes it ideal for single-sided access installations. What size fastener does this pad accept? The tapped hole is 5/16"-18 UNC — use a 5/16"-18 stainless bolt or machine screw for a secure threaded fit. Can I use this on a fiberglass deck? Yes — the pad distributes fastener load across a wider surface area, preventing pull-through or deck damage. Thread the bolt into the pad from the exterior side; the pad threads hold it securely. How is this different from a backing plate? A backing plate has straight through-holes and requires a nut on the back side. A tapped pad has internal threads — the fastener screws into the pad itself, so no back-side nut is needed.