Circle wedges are a must for all heavy hitters.
there are a number of variables that make the handle-to-tool fit as secure as possible:
1. using a riffler to fit the wood that will be in the tool's eye as form fitting as possible
2. a good wood wedge that is driven as deep as possible
3. using a white wood glue on the wood wedge so when cured become one with the helve's wood
4. giving the wood in the eye a good soak in linseed oil to protect from drying and shrinking
5. when extra security is needed then a circle wedge finishes the job (done before the linseed soak)
the idea behind the circle wedge is to push the wood in all directions. this multi directional pressure is more secure the linear pressure delivered from a pick style metal wedge.
circle wedges usually come in large sizes
are perfect for tools that take more impact abuse: mauls, sledges, large double bits and so on.