Insulator for LM3886T

What about a strip of "Selotape"?
If the chip never gets hot, the Selotape will never degrade.

You are joking right?!
The point is to get electrical insulation and excellent thermal conductivity. I don't think a strip of sellotape (aka "scotch tape" for Americans) will provide good thermal performance. And the electrical isolation is iffy too. As it gets hot, and it will due to bad thermal conductivity, it will probably melt and could allow the chip's tab (at -Vcc) to contact the heatsink (usually at gnd). Boom!
I am not joking.
I recognise that sticky tape for fixing parcel wrapping is not a recommended Thermally conductive and Electrically insulative and Temperature tolerant interface material.
But in the short term for OBSERVED testing it works and it works well.
Try it.
It is a good Electrical insulator for typical SS amplifiers, i.e <100Vdc
It is a good Thermal conductor compared to real tapes. Not as good as thin mica, but certainly better than 6thou Kapton and 5thou mica.
It does tolerate the lower temperatures of warm to very warm heatsinks. I would not use it for a too hot to touch heatsink.
I would not use it for hidden use long term inside a chassis.
Thanks for the tips guys.

TO-247 looks like a good idea. I don't care that it is over-sized. I have done a bit of digging and it seems a TO-218 washer will work on a TO-247 chip, so it should also be usable.

AndrewT, I am looking for a permanent installation, so sellotape is not my best solution, but thanks for the tip!

I am looking for a 'proper' solution that is big enough, has its hole in a usable location with LM3886T, and can be purchased.

Does anyone know why the TI datasheet says the LM3886 is a TO-220 package? It seems misleading. (I actually bought a bunch of TO-220 insulation washers to use with my LM3886 purchase, based on the TI datasheet, and only saw their inadequate size once I got them).
just clicked on post9 link.

That Seller does not mention thickness nor Thermal Resistance/Conductivity.
In other tape items they sell, the same product is listed as 330mm length, 12.99feet length, 33m length and finally 108feet length. Does the reel have 330mm or 33000mm on it?
The Seller does not know their product !!!!
What kind of customer support would one expect from a Seller like this?