The 'Fix' tyres, the 'SIT' tyres, the 'Easy Fit' tyres, the 'Click' Tyres and the 'Clip-lock' / LIP tyres: they all mean one and the same.
The bead portion of the tyre is slightly modified & extended into a small nipple: but this is the most critical portion, as its durability has to be next only to steel in terms of its tenacity.
Eventually this lip goes to replace the locking ring (made of special spring steel and hence slightly risky to fit on a solid tyre) in a multi-piece Pneumatic tyre rim. The lip fits snugly into the space otherwise filled & held by the steel lock-ring.
So, when you are looking to replace the Pneumatic Tyres that come fitted with your new forklifts, you can eliminate the need to fix the lock-ring and instead opt for solid tyres with clip-lock rim profile.