Glazier's tool placed neatly at the start, if held by Yorkshireman (5-5)

'glazier's tool' is the definition.
(I've seen this in another clue)

'placed neatly at the start if held by yorkshireman' is the wordplay.
'placed' becomes 'put' (I've seen this before).
'at the start' indicates taking the first letters.
'held by' is an insertion indicator.
'yorkshireman' becomes 'tyke' (tyke can mean someone from Yorkshire).
The first letter of 'neatly' is 'n'.
'n'+'if'='nif'
'nif' placed within 'tyke' is 'tyknife'.
'put'+'tyknife'='PUTTY-KNIFE'