To opening nuts, wrench is used for this. The nuts can be made by brass, zinc, steel or aluminum. The fishing reels are usually has brass or zinc nuts. My prefer for nut wrench is open-end or combination model. But you can use adjustable models as your prefer.
Combination Nut Wrench
This is 13mm combination nut wrench that made by chrome vanadium. Manufactured by Stanley. With this 13mm wrench, you may remove nuts up to 1000-4000 model of spinning reels on the market. I usually use this nut wrench on Daiwa and Shimano spinning reels.