I believe this to be a rather rare webbed frog for a VZ24 bayonet.   It is pictured on the left, a webbed frog for a standard SG84/98 is pictured on the right.

Below is a VZ24 bayonet inserted into a SG84/98 frog.  You can see how loosely it fits.

Below is a SG84/98 bayonet inserted into the VZ24 webbed frog.  It has been pushed in as far as it will go without damaging the frog.

Below is a VZ24 bayonet inserted into the VZ24 webbed frog.  You can see how well it fits.