I'd posit that there is no need for an initial depression with soft wood like a pine 2X4 (in us it is a reference for non dimensional lumber and painfully it is imperial 2 inches * 4 inches before drying) 38X63mm soft wood stud? The wood should give way to plastic deformation as the brass washer does, and being in the middle, should both contour the ball bearing together! It's old now, a wet one left outside to freeze , if the wood is to soft