Per Brian Nystrom:
As Pete said, use circular plastic containers of appropriate size
to stretch the latex gaskets before glueing.

What possible advantage could there be to doing that? Seals come in
stock sizes that are designed to be glued to garments made in the same
sizes. If you did manage to stretch a seal somewhat, you would simply be
compromizing the fit of the seal to the garment. You DO need to use snug
fitting forms in the garment when replacing wrist and ankle seals or
installing latex socks. The purose is to create a smooth surface and
prevent bunching of the material, not to stretch the seal.

Possible semantics issue. I don't use the Ricotta cheese containers for
stretching in the sense of making the gasket larger, just to provide a stable
foundation for bringing gasket and sleeve together. What's handy is the light
taper in the container - just put it inside the sleeve and slide it out until
the sleeve is taut and then place the gasket over top of the taught sleeve's
surface.
--
PeteCresswell