So instead of buying a small number (25) of the right size bolts I ended up buying a whole multi-pack of assorted sizes for rather more expense, because that was the only option. And why do bolts come in packs of 10 or 25 whereas the nuts only come in packs of 100?
So I ended up buying the following:
Screwfix sub-total = £24.30
- countersinking drill bit, part 11311, £5.37
- machine screw pack - for 12 countersunk 5 mm diameter bolts at 2 cm length for fixing rails/angles to MDF - part 13352, £14.99 (ouch)
- 5 mm nuts, pack of 100, £3.94
Running total = £97.02
Unfortunately, I forgot to get the 8 mm nuts to fit the threaded rods......