Crocket hooks are used to make it easier to attach a rubber motor to a winder and prop hook after winding.  The Hook also help eliminate the tendency for the rubber motor to climb over the prop hook and knot up causing the prop to stall and stop rotating.  It allows the rubber motor to flop and spin inside the fuselage.  I don't personally use one.  I usually use a reverse "S" hook on the prop shaft and use "O" rings on the end of the motor to allow easier attachment to the winder and prop hook (reverse "S" hook).  I'm also using a double tube setup on the motor anchor as well to eliminate the motor climbing the motor anchor tube and bunching up in the tail end of the fuselage.  Check out the tips and tricks section for further tips on rubber motors etc.

Found this link on the NFFS (National Free Flight Society) re: crocket hooks Click Here
Another alternative to crocket hooks: Click Here
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