Rubber Plug

[BonesD]

Howdy, I removed a device from my exterior cabin ceiling which has left two .75” holes. I want to temporarily plug and seal the two holes as I may find a use for them.
I have been looking for a rubber/silicone/ plastic stopper that looks a bit like the hand drawn picture below.
I would like the shoulder on the plug to be about a 1/4 wide but if smaller no less than ..125”.
I know I’ve seen stuff like this but can’t seem find anything beyond tapers rubber plugs or very small plastic cap. Kind of like a champagne corks with a bigger top
Anybody?
Thanks

 

[bayview]

You could ignore the hole size and use SS fender washers and round head bolt with an acorn nut

 

[jleonard]

Perhaps?

https://www.mcmaster.com/plugs/plugs-4/plug-type~push-in/for-hose-id~3-4/

 

[BonesD]

Many ways to plug it. Just looking for something the least possible chance of water leakage. I will also be replacing the interior ceiling and two less bolts sticking through will be better.

 

[HopCar]

These make a water tight seal. I’d put a little sealant or locktite on the threads just to be sure.
https://www.mcmaster.com/well-nuts

 

[Xsbank]

Bevel the hole and with a little sealant (I would use butyl) use a flat-head machine screw and an acorn nut below, or no nut at all. Then it will be flush. I had some aluminum fasteners for a project and they had a nice hex head. McMaster's, I think.

 

[sbman]

For a semi temporary measure I'd use a hole saw to cut a piece of starboard the proper diameter. Remember that the inside of your holesaw contains the part you want and you'll need a bigger hole saw than it is specified for, because the spec is on the outside diameter of the hole saw the piece inside is at least 1/4" smaller. After making my round plastic with the hole saw, some sand paper or a sanding pad in an angle grinder can clean up and taper the edges to make it more like the mushroom cap you are looking for.

Then use the center hole in that new round piece of plastic with a stainless steel cap head screw through the top to bolt it into place, bedding both the screw and the starboard with butyl tape. A nut and washer on the inside keep it secure.

If aesthetics matter on the inside, you can cut the stainless steel screw to just the right length and use an acorn nut for a nicer finish. Could also cut another round piece of starboard and shape it for the inside to use as a 'washer' if a decorative appearance matters.

Would make a watertight seal for a long time and yet be easily removeable and clean up with just some mineral spirits.

 

[AusCan]

I would epoxy them up. Easy enough to drill them out if you ever find a use for them.
Temporary fixes often get forgotten about.

 

[Comodave]

I would epoxy them up. Easy enough to drill them out if you ever find a use for them.
Temporary fixes often get forgotten about.

Absolutely. I would epoxy them closed with thickened epoxy. Those plugs are going to leak. And as said it is easy enough to drill the plugs out if you need to. 15 minutes and it will be done.

 

[BonesD]

Thanks for all the good suggestions. I’ve got it sealed up for now until I decide what I want to do with holes. I may use them to mount some hardware in the future.