So instead of a Train Driver, or Fireman as I'd have started as, I became a Builders Merchant's Apprentice. Got Certificates for it, know how many fletton or Class A Staffordshire Blue bricks in a ton, the British Standard for Cast Iron Manhole Covers & Frames (BS 497 it used to be, & the old Double Triangular was my favourite),
Un-interesting facts about manhole covers number 275
You cannot drop a round manhole cover down its own hole, whereas you can with any other shaped one.
What about a single tringular?