These cup seals consist of high-strength resin bodies and high-quality cup seals. Available in both 1/8" and 3/16" shaft options: 

1/8" Seal: 
Outside diameter: 10.35mm 
Length: 15.6mm 
3/16" Seal: 
Outside diameter: 11.9mm 
Length: 16.4mm 
 
To install:
Drill a hole equal to the outside diameter of the seal in your bulkhead.
Press the seal body into place with the small opening facing toward your watertight compartment.
Secure the body with thin CA. Put a bead of glue around the perimeter of the seal body where it meets your bulkhead.
Insert the cup seal into the body with the flat face toward your watertight compartment
Place a thin bead of clear RTV around the perimeter of the seal cap
Press the seal cap into place, wiping any excess RTV off with a rag
Let cure for at least one hour prior to use
 
If the seal ever becomes damaged or leaks, pry the cap off, pull the old seal out and install a new seal, following instruction steps 4 thorugh 7.