U-Bolt AISI 316 with Two Backing Plates – Various Sizes (Length 80–155 mm)

U-bolts are one of the most versatile fasteners on any boat. Made entirely of high-grade AISI 316 stainless steel, these U-shaped bolts offer exceptional strength and corrosion resistance, even after years of exposure to the marine environment. Each U-bolt comes with two rectangular reinforcing plates (washer plates) with pre-drilled holes – one plate is placed on the outer side and the other on the inner side of the mounting surface. This double-plate design spreads the force when the nuts are tightened and prevents damage or indentation of the surface (for example, your deck, transom, or railing) under pressure.

Our selection includes multiple U-bolt sizes to meet different needs:

• Small sizes (length 80–90 mm, thread M5/M6): Suitable for lighter applications – securing cables, hoses, small railings, or serving as lashing points for canopies and gear. For example, an 80 mm U-bolt (M5) can be used to fasten a rescue line eye or a flagpole base.
• Medium sizes (length ~105–110 mm, thread M8/M10): All-purpose U-bolts for medium loads. They are ideal for installing grab rails and lifelines (tube diameter ~22–25 mm), fixing seat pedestals or console frames, and bracing movable parts such as ladder hinges. For instance, a 110 mm U-bolt (M10) can securely hold a support bar or even help mount an outboard engine to a bracket (using multiple bolts as required).
• Large sizes (length 135–155 mm, thread M10/M12): Meant for heavy-duty tasks requiring maximum strength. These U-bolts are suitable for attaching major structural components – for example, an anchor windlass base plate, structural ribs, or even a trailer chassis. A 155 mm U-bolt (M12) with large backing plates (100×25 mm) can serve as a robust lifting/towing point or clamp around a thick beam or post.

Example Uses & Tips:

• Rigging & Deck Gear: Use a U-bolt to secure a block or pulley base to the deck – the backing plates will distribute the load from a taut rope, preventing damage.
• Tie-Down Points: Install multiple U-bolts along the gunwales or in the cockpit as strong tie-down loops (pad eyes) for docking lines, gear, or cargo (e.g., strapping down an inflatable dinghy on deck).
• Trailers & Engines: U-bolts are extensively used to attach boats to trailers – wrapping around trailer frame beams and holding keel pads or rollers. The stainless steel ensures no ugly rust streaks on your hull during transport. They’re also useful for mounting outboard motors or engine hoist rings where a secure clamping is needed.
• Easy Installation: Choose the location and drill two holes at the appropriate center-to-center distance of the U-bolt. Insert the U-bolt, place the backing plates on each side, and tighten the included stainless steel nuts. Tighten evenly so the plates sit flush – this gives you a secure, non-slipping attachment. We recommend adding a bit of sealant or rubber gasket under the plates if mounting on fiberglass, for extra waterproofing and cushioning.
• Safety: All edges of the U-bolt and plates are smooth and rounded, which protects ropes and sails from chafing. Ensure the exposed threaded ends are capped with acorn nuts or covered with tape to prevent accidental scrapes or snagging.

By choosing these AISI 316 U-bolts with twin plates, you’re investing in a durable, multi-purpose fastener that won’t let you down. They combine strength, resilience, and practicality, making them an essential part of any boat owner or builder’s hardware kit for retrofits and upgrades.