It’s really a device for ‘first icers’ so that they can check that the ice is safe in front of them. It’s a heavy steel bar with a sharp wedge as described above, and you thunk the point into the ice in front of you as you walk along using it like a walking staff.
A good homemade one is a busted blade off of a chisel plow welded onto a piece of pipe around 6′ long. The T handle at the top keeps it from slipping from your hand and going to the bottom if it punches through. A couple years ago we were walking along and the lead guy was spudding the way; he punched it through and with no handle, down it went.
What followed was truly hilarious – he stood there on about one inch of ice and bitched for what seemed like ten minutes about losing the spud bar, all the while the rest of us were sloooooowly edging back away from him. When he realized what was happening, he made tracks back toward us as well.