[chrismortimer66]

You can use wrist roller devices in a gym, they can help. but best exercises I have seen and practiced for wrist strength is what arm wrestlers use, these guys have the strongest forearms and wrists you'll ever find.
1 good techniqe is to get a 3-4 foot bar and atach weight to the end, grab the other end, and with you hand by you side raise the bar up so your lifting the weighted end upwards. you can hold the bar with the weight behind you and move the weight upwards in that manner too, and finnaly you can grab the bar in the middle holding it infront of you [bent not straight armed] with the attached weight pointing up and twist your wrist from left to wright.
do each one of these type excercises 1-2 times a week, 9-12 reps and 2 sets, should set you up for havin quite good wrists.
If what I have written doesn't make sense, look up arm wrestling training, and you will find all you need on wrist and forearm training.

Also don't overlook training on a heavy bag [100lbs+], this will definitly help.
hope this helps.