Complementary Hardware - Inspection Ports

Sailboat Inspection Ports: Screw-Out, Twist-Out and Threaded Types, Sizes and Cut-Out Holes

An inspection port is a round access plate set into a deck, locker or bulkhead so you can reach a valve, a back-fastening, a tank or a bilge without removing anything. This collection covers two families: Beckson deck plates in 4, 5 and 6 inch sizes, and Ronstan threaded inspection ports of 106 and 125 mm. The choice comes down to the opening size you need, how the cover opens, whether you want a clear centre, and the cut-out your deck can take.

Inspection Port Families in This Collection

• Beckson screw-out deck plates, clear centre: the DP40-W-C (4 in) and the DP60-W-C (6 in), both in white. The digits in a Beckson model number are the plate size in inches: DP40 is 4 in, DP60 is 6 in. Beckson describes them as designed for access without tools, with a single-start non-jamming buttress thread, a self-aligning centre, and a gasket plus a back-up sealing wall that keeps the plate water resistant even if the gasket is removed. The clear centre lets you see a gauge or a control without opening the plate.
• Beckson Stow-Away deck plate: the DP50BW is Beckson's 5 in deck plate in white with a nylon bag. Beckson's 5 in plates open with a quick twist-out, not a screw-out. The bag has a sewn-in rigid ring that seats in the plate, so the plate doubles as dry storage for small items such as keys or a watch, and the bag lifts out when you need access below.
• Ronstan threaded inspection ports: the RF530 (106 mm internal diameter) and the PNP97 (125 mm class, 129 mm internal diameter). Both are white threaded ports moulded in impact-resistant, UV-stabilised nylon, for access to areas under decks or behind bulkheads.

Cut-Out Sizes to Plan For

• Beckson DP40-W-C (4 in): hole cut 4 1/2 in (11.4 cm).
• Beckson DP50BW (5 in): hole cut 5 1/2 in (14 cm).
• Beckson DP60-W-C (6 in): hole cut 6 1/2 in (16.5 cm).
• Ronstan RF530 (106 mm internal): cut-out 122 mm.
• Ronstan PNP97 (129 mm internal): cut-out 139 mm.

The Beckson hole sizes are Beckson's published hole-cut figures for each plate size; the Ronstan cut-outs are the figures in our product listings. Confirm the cut-out on the product page before you cut, and allow for the outside diameter of the flange (148 mm on the RF530, 170 mm on the PNP97) when you pick the spot.

Screw-Out, Twist-Out or Threaded: How to Choose

• Screw-out (Beckson 4 in and 6 in): the cover threads in and out without tools. Beckson recommends a screw-out plate in compartments where a change in air pressure from temperature or oil-canning can occur. It suits access to shut-off valves, back-fastenings, inspection and clean-out of tanks and compartments.
• Twist-out (Beckson 5 in): opens with a quick twist and conceals the mounting fasteners under the cover. In this collection it is the Stow-Away plate with a bag.
• Threaded port (Ronstan): a nylon body with a threaded opening and a removable cover. Ronstan describes it as access to areas under decks or behind bulkheads.
• Clear centre or solid: a clear centre lets you check a gauge, a valve position or a leak at a glance. A solid cover is the choice when you only need access.
• Fuel tanks: Beckson does not recommend its screw-out plates for direct access into a fuel tank, because diesel can degrade the moulded O-ring. Mounting one in the deck above a tank is acceptable. For a tank opening Beckson suggests an aluminium or stainless plate with diesel-compatible gasket material, bolted through the tank.

Who It's For

Owners adding service access to lockers, tank tops and bulkheads, refit projects that need a clean opening over a valve or fitting, and anyone who wants a dry stowage spot on deck. For the Beckson plates on their own see Beckson inspection ports. If you are choosing a portlight rather than a plate, read how to order Beckson Newport ports.

Frequently Asked Questions

What size hole do I cut for a Beckson deck plate?
Beckson lists a hole cut of 4 1/2 in for the 4 in plate, 5 1/2 in for the 5 in plate and 6 1/2 in for the 6 in plate. The number in the model name (DP40, DP50, DP60) is the plate size in inches.

What is the difference between a screw-out and a twist-out deck plate?
A screw-out plate threads in and out and needs no tools; Beckson recommends it where air pressure can change inside the compartment. A twist-out plate opens with a quick twist and hides its mounting fasteners under the cover. Beckson's 4 in and 6 in plates screw out, and its 5 in plates twist out.

Can I use a Beckson screw-out plate to access a fuel tank?
Not for a direct opening into the tank. Beckson says diesel can degrade the moulded O-ring and cause leaks. It does accept a plate fitted through the deck above a tank, and suggests a metal plate with a diesel-compatible gasket for the tank opening itself.

What does the Stow-Away deck plate hold?
The DP50BW comes with a 12 in nylon bag with a rigid ring that seats in the 5 in plate. It is meant for small items such as keys or a watch, and the bag removes so you can reach what is below the deck.

What are the Ronstan inspection ports made of?
Both the RF530 and the PNP97 are impact-resistant, UV-stabilised nylon with a threaded opening, white, and are meant for access under decks or behind bulkheads.

Related reading from our How-To Guides

• How to Order Beckson Newport Ports