This is a fly wheel locking tool used when changing a cambelt.  NB: These are for 1.8 engine manual gear box only.
The correct way for locking the crank when tightening the crank pulley bolt.  ( 110 N/m )
Of course you could save yourself a few quid by jamming something in the flywheel and risk doing some damage or use a impact gun to lock up the crank bolt and risk overstressing the timing belt ..and the crank pulley working loose..but why would you?
Designed and made inhouse.