Smallest dust caps I can find are 35mm (1.38inches) - slightly too big but I think these would be acceptable?
Unless of course anyone knows a source for 25mm (1inch) dust caps?
And then of course there is the next question of which glue to use. I would tend to favour PVA while others have used Aleene's Tacky Glue but has anyone used this stuff: -
https://www.ebay.co.uk/itm/Black-505...L/392873719769