Clue: Worthless old 13 — no parts? (2,2,3)
Answer: OF NO USE
Explanation: Definition: Worthless
An envelope ('parts') of 'no' in O ('old') plus FUSE ('13' TRIP SWITCH i.e. a circuit breaker – the word FUSE is still used loosely in this sense – you would still go to the fuse box to find them).