Serial brushed motor and rpm running wild.

Hello.

Ive heard that serial brushed motors will spin to death if not applied resistance.
And if the chain breaks they will destroy themselves kmin seconds.

Ive heard i can attatch some sort of overspeed protection
What is that and where can i buy those?

Why not a permanent magnet motor?

Because i have Forklift motor

Here's a sampling of centrifugal switches. One of these operating a normally closed contactor might do the job. You'll have to find something that works with your motor shaft and your required cutoff RPM.

https://www.amazon.com/gp/aw/s/ref=is_s?k=centrifugal+switch