help needed silicone o rings

I am in the process of building a 70 litre stockpot boiler (sorry about the metric ) using a camco 4500 element and an aluminium box as element terminals protection.
I want to fit it like the electric brewery site suggests
I ordered some 1 1/4 inch red silicone o rings from a site on ebay but they are much too thick (about 5mm,7/32") I think the mcmaster ones are 1/8"(3.17 mm).
I cant get the nut to start on the threads.The box is 3/16 thickness wall
,I think I maybe need the correct box and covers and 1 1/2" shim
can anyone give me a site where I can order the correct size ones from as mcmaster ship to greece (I e-mailed them)
or could some kind person order them for me and send them on to me .
I will pay for them before you order by paypal
thanks paul

does anyone know of a supplier in houston texas for these o rings and shim as I have a uk contact there until friday so not enough time to post things but if he could just go and buy it he will

thanks Paul

Grainger in Houston should have the o-rings in stock.

thanks for that jcosbrew

PM sent

thanks to all who contacted me .I found the o rings and washer on amazon USA site thanks for the links JCOSBrew
Paul