I've tried studs and bars from lots of companies including Simms and Patagonia. These Orvis Posigrip studs are the best I've tried. They grip well and they last a much longer time than others I've had experience with. They also don't pull out of your boots nearly as easily. Make sure to put them around the edges in the front of your boot instead of the middle. The screw is long enough it can poke through if you place them under the ball of your foot.
Aggressive tungsten-carbide tipped screw-in studs that can be added to any wading boot with at least ½" of midsole depth. Sharp tip allows for quick and easy installation into felt or rubber outsoles. A must where maximum traction is needed. ¼" hex head screws. Adapter for power drill included. 20 studs per pack. Made in the USA.