I look at the presence of these small holes in the cross guard of my No5 & No7 bayonets from an engineer's perspective not a soldier's. I assume that they must have been included during production for a reason and so I start looking for possible explanations/solution from an engineer's perspective. Aragorn243 has made a very good suggestion as a likely reason for the holes being there looking at it from an engineer's viewpoint, possibly more likely than mine of wiring the bayonets onto the rifle.