Go for the 1/8th. The surfaces are too thin for the 3/16th. You are better off using smaller hinges that have more 'meat' around them. I use Robart's almost exclusivly now. 1/8 on everything from 40 size all the way up to my GP Skybolt with a Magnum 120.

Have any of you ever done a pull test on a Robart hinge? 20 pounds breaks the 1/8. But just one. Multiply that by three for an elevator half, and you have 60 pounds of tensile strength for one control surface. If the plans call for 3 CA hinges on an elevator half, replace them with 3 1/8th or 3/16 if the thickness allows.

I also use poly glue to mount them in. Never had a failure.