Be able to hear a pin drop used to describe absolute silence or stillness.
clean (or neat) as a new pin extremely neat (recorded from the mid 18th century).
for two pins at the slightest provocation (a pin here as the type of something of little worth). Recorded from the late 19th century.
see a pin and pick it up, all the day you'll have good luck; see a pin and let it lie, bad luck you'll have all day proverbial saying, mid 19th century, extolling the virtues of thrift in small matters. A similar idea is found in an older proverb, recorded in Pepys's diary for 2 January 1668 as quoted by Sir William Coventry (1628?–86), ‘He that will not stoop for a pin will never be worth a pound.’
See also how many angels can dance on the head of a pin?, needles and pins at needle, it's a sin to steal a pin.