What's this sticky tape called?

Adrian Caspersz explained :

I know just what you mean, but sorry I cannot think of the name..

Replica tape.

harry presented the following explanation :

I had in mind the material which compresses, so that measuring its thickness once the two surfaces are disassembled = you know what the clearance is between the faces.

Plastigauge?

Kevin explained on 10/07/2019 :

That is the one I had in mind..

Isn't that plastiguage ?

But it looks nothing like decorators masking tape

Lead wire was an older method I have seen used to check the bearing clearance on a ships triple expansion engine. The engineer , the engine and probably the reel of the wire all dated from before the plastic age.

GH

Never heard of that (although I spent years measuring rough surfaces, including taking replicas).

Our replica material of choice was Acrulite, this is just methyl methacrylate monomer which you mix with powdered polymer. It sets in a couple of minutes.

You can also get replicas using RTV silicone, either two pack putty as used by dentists for replication, or creamy liquids dispensed from a double tube syringe through a mixing nozzle.

Metallurgists have a clever technique for large, immovable plant. They grind and polish the surface finishing with micron diamond paste, then etch, then apply a drop of acetone and press a thin piece of acetate sheet on to the surface, and allow it to dry. Done well, the resulting replica, examined in a metallurgical microscope, gives almost as good an image as could be obtained from the original metal.