All Snapdragons and I suspect all or nearly all Mirages were built using Imperial Whjtworth thread bolts, the sizes being 3/16”, 1/4”, 5/16” and 3/8 with the occasional larger size. Whilst these are still made they are all but impossible to buy at the local chandler’s
If you need to replace any, then a search of Yellow Pages under ‘Bolt and Nut Stockists’ may yield a supplier near you, however some may only sell in full boxes, which could mean 100 or nothing. For those on the East Coast I can recommend South Essex Fastners’ with branches in Southend and Colchester, and certainly the Colchester branch is prepared to sell you a single bolt if you need one.
The alternative is to replace with metric bolts of the nearest diameter. You can work this out with a calculator if you remember that one inch is EXACTLY 25.4 mm. So a 3/16” bolt is 25.4 divided by 16 and multiplied by 3, giving 4.7I mm, an M5 bolt will do if you ease out the hole slightly with a 5mm drill.
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1/4” is more of a problem as this is 6.35mm, so an M6 whilst adequately strong, is rather a slack fit in the hole and could cause leaks. Opening out to M7 would be best but this diameter is not likely to be available at the local chandlers. 5/16” is fine at 7.93mm, as probably an M8 will go straight in without using an 8mm drill. 3/8” is also easy at 9.53mm, as slight easing of the holes will accept the readily available M10.
Chasing out with a metric plug tap will usually improve the ‘fit’.
If you need long hex head bolts and have difficulty In getting them, then you can buy metre lengths of stainless steel studding from suppliers like South Essex Fastner ’s at ridiculously low prices,. Cut the length you need and use a nut at each end.
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