tank hatch terminology

Are you talking about Helicoil inserts?

http://www.helicoil.in

Google "thread inserts" there is many different styles

The threaded part is sometimes called thread-certs. Not sure what the backing plate with them in it are called. You might want to just have a few thread certs welded into what you have. I don't think you can buy the backing plate with them in it anywhere. Might need to have a machine shop make it.

I must be missing something. I don't even see any threaded bars in those pictures. Just what looks like threaded inserts in the fiberglass.

I tend to agree with CaptJ that what you have theRe was made for the job in the quantity required.

It should be fairly straight forward to remove them and have a machine/welding shop make you a set or two the same.

You could also just use thicker Alu bar and drill and tap them yourself but you would not get what looks like those little stand prouds that are flush with the fibreglass surround.

If its only a few that are stripped it might be a lot simpler and economical to Helicoil them and use plenty of Tef Gel or similar to negate any action between Alu and stainless if this is the fastener material.

Looking at the photos this looks to be a fiberglass tank flange arrangement using 1/4-20 flat heads counter sunk flush holding aluminum
flat bar under the tank opening to form a reinforced flange. The fiberglass has thread certs screwed / glued (5200?) into the glass. It would be my assumption that the thread certs are also tapped into the flat bar for added strength. As far as nomenclature goes? "tank manhole bolt flange"?

I think CaptJ hit it. It's simply a backing plate. K1W1 also when he said just make up a new one. Any welder or machine shop can make it up out of flat stock. If you search catalogs or walk around a hardware store you may find one similar that's made for some other purpose as well.

Built the same thing for as fuel tank hatch many years ago. The AL bars are threaded for the cover bolts. The bars are held in place using a couple of flat head screws while the cover is off.

Bob

It sure looks in the photos like there is Alu that sticks up right to the level of the fibreglass. This is why I suggested using a thicker flat bar to allow for some thread depth.

The first picture clearly shows the Phillips flat head screw that is holding the backing plate in place. The threaded inserts look like some type of captive nut. I used those to keep from having to tap the aluminum and possibly stripping the aluminum threads. Look at McMaster-Carr for captive nuts.

Bob

They could be something like this inserted from below the flat bar: http://www.memfast.co.uk/shop/Vprod2.asp?cat=2252003316

If so it should be possible to drive or press out the stuffed ones and insert new ones.