Tire Iron BeadBrakR slide show - BestRest
The big wooden block with the slot is designed to fit a tire iron placed on edge.  This keeps the TIBB standing upright when you're lowering a tire into place.

The big wooden block also acts as a "sand foot" when using the TIBB in soft field conditions.  It prevents the TIBB from sinking into soft earth

The big wooden block with the slot is designed to fit a tire iron placed on edge. This keeps the TIBB standing upright when you're lowering a tire into place.

The big wooden block also acts as a "sand foot" when using the TIBB in soft field conditions. It prevents the TIBB from sinking into soft earth