Most of the locking caps I've seen come as a whole assembly.
You can try something like this that prevents siphoning from the fill:
http://www.vetusmarine.com/store/p/387-Fuel-Theft-Security-Device.aspx
I've used Teflon paste sealant on the plugs for years & never had a problem with leaks or removal.
https://www.homedepot.com/p/Hercules-Real-Tuff-4-oz-Pipe-Thread-Sealant-156152/203304169
Interesting that a 25' would be considered over the 5 NT. I just did a search through the USCG PSIX and found more than a few 25' Parkers that are indeed documented. Its looks like most of them use 4.5' for the depth measurement so if go by that measurement it would be around 7+ GT so I guess...
Brackets don't count, the pilothouse doesn't count, anything in the hull such as fuel or water tanks would subtract from the volume.
Search for USCG form CG-5397. Truthfully save yourself the trouble as any boat under approx 27 ft will not be 5 NT
Tonnage as related to documentation has nothing to do with the weight of the boat. Its the volume in area the vessel can hold.
There is a formula the USCG goes by. Basically its Length x Beam x Depth (Rub Rail To Bottom Of Hull) x .67 For Powerboats
Wish someone made these in stainless. Years ago there was a company on Ebay that had a exact stainless model but it wasn't a reverse bevel like the OEM Perko 0919.
Anyone looking to replace the Perko the cheapest I've seen is Walmart...
A couple of things I found going through boxes. All is free, just pay shipping for whatever you'd like & PP fees if sending goods payment.
*** GONE *** Rail Mount Clamps - Fits 7/8 And 1" Rail (NEW IN PACKAGE)
*** GONE *** (4) Merc Prop Tab Washers (NEW)
*** GONE *** (2) SeaStar Steering...
SOLD
YAMAHA OUTBOARD OEM PROP HARDWARE
The Thrust Washer & Cotter Pin Are New The Other Parts Are Used
Spacer: 688-45997-01-00
Castle Nut: 90171-18M04-00
Cotter Pin: 91490-40030-00
Washer: 92990-18200-00
Thrust Washer: 63P-45987-00-00
I don't know if the springs are different year to year but for my 1997 2320 I bought some years ago from a window hardware company.
Similar to these:
https://www.primeline.net/pl-14624-flat-springs-2-58-spring-steel-zinc-plated