Step down rings

[vilipertti]

I need a step down ring for my Raynox 3031 wide angle lens. Lens comes with a 37-43 adapter, but it's so 'thick'. I've noticed, that the closer WA-lens is to Canon lens, the less it get blurry and vignetted towards the edges.
Do you know, is there any thinner step down rings available?

[Murrelet]

I got (I think it was, hard to tell as the packaging was very old, clerk found it at the back of a junk drawer) a Tiffen step down for my old Sony WA from my Hi-8, 43-37mm. When screwed into place it's 3/32" thick from the camera with the inner threads going all the way through. All told it's about 3/16" thick overall.

When the Sony WA is screwed into place the back of the glass on the WA matches the outer face of the step down. So might be roughly (as I'm sure the measurements are all metric) 3/32" further out than the WD-H43, which seems to align the back of that lens with the front edge of the HV20.