After trying several types of materials to make spacers that have included HVAC tape and or automobile pin-striping material, IMHO here is the best material that I've come across yet so far.
See these links for product that I use. It is the silver foil color that is bright silver which closely resembles the original spacers. I'm a stickler about wanting the spacers to match as close as possible to the original ones used.
Silver Foil Adhesive Material for Telescope Objectives Needed 0.003" Spacers.
Stainless Silver Foil Adhesive Material for Telescope Objectives Needed 0.003" Spacers.
With that said, they also make a silver stainless material that I have bought, but have not tried yet. That may even be a more perfect match to the original spacers as it may be a slightly less bright silver color.
This material is very easy to work with. Colors are called "Silver Foil" and Stainless Silver".
This material is now what I use and it is sold at different craft/hobby stores here in the USA and even Australia.
The material is within a few tenths of 0.003" which includes the extremely thin non messy adhesive on back side.
IMHO much better than HVAC type which has too much adhesive on the back side. Also better than the Flue Tape which is too sticky, so less forgiving to place in the exact location.
From what I've worked on, the majority of Astro Optical and Swift etc objectives appear to have used 0.003" material best I can measure.
When you peel off the white backing paper from this foil, there is a very thin amount of self adhesive on the foil. After peeling off the backing material, the thickness is 0.003" with Calipers and 0.0285" with a Micrometer.
Cut longer/wider piece than needed with a very sharp Fiskars brand or like type of fabric scissors and then trim with a new razor blade to exactly match the size of the orig spacers. Use the new single edge razor blade to peel off part of backing on the piece trimmed. Use special tweezers to gently hold material and set the spacer in the correct location. Then use the end of a rounded toothpick to gently finish adhering the foil to objective.
It helps to have a hobby magnifier that I wear on my head and flip down over my eyes and or reading glasses similar to what a jeweler uses for close up work. I need stronger magnification than my reading glasses to see real close up to locate the spacers in the correct location just off the beveled edge of the objective for the spacers that do not overlap the edge.
Your mileage may vary as they say, but I've had excellent results so far with this material.
Edited by Stargoat, 22 January 2019 - 09:31 PM.