If you have a faithful Acorn Risc PC kicking around you might have found that the rubber feet on the bottom of the case have started to crumble, like mine:

In some cases the rubber feet can even liquefy and leave you with a wonky computer sitting in a pool of grey goo.

You’ll be pleased to know that you can lever off the old ones and replace them with a new set of Bumpons (that’s what they’re called) from 3M.

The specific ones you want are 3M Bumpon SJ5023 in grey. They’re 20.5mm² wide by 7.6mm high. The datasheet is here. I bought my replacements from an eBay seller. Note that the greys seem harder to find than the black and clear variants. [2021 update - RS have them: https://uk.rs-online.com/web/p/anti-slip-pads/0236537/].

Once you have your replacements, start removing the broken feet. Avoid damaging your antique computer by working a blunt knife in at the corner closest the edge. Then push up to lever the old foot out.

This is made easier since the holes for the case locking pins go right through the case and leave a void under the foot; the bumpon’s flat base never entirely adheres to the full square.

Once removed, clean the old glue off using some isopropyl alcohol. I used a toothpick too for the harder gunk.

Cleaned:

Then you can peel off the new feet/bumpons/tapered squares/trapezoidal prisms from their backing paper and fit them:

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