5mm didn’t slide into the rails on my Creech, I had to remove the side rails and reverse the glass slides before it would fit properly. I think the original glass is nearer 4mm.
I have some spare sheets at Flip Out London in Croydon. I've replaced all mine with invisiglass. Make me an offer and you can collect it when the club is open, Thursday nights, Saturday and Sunday afternoons, or by arrangement.