Following my recent tumble I had to purchase a new rear indicator. I fitted it last night and found that there was no screw for fixing the lens cover in place to the body of the indicator. I have snapped the cover into place and it appears to be held firmly in place with the plastic tabs so is this the way it is meant to be now? Is the screw fitting redundant and the plastic tabs considered to be sufficient to retain the lens cover in place? 
I thought about putting a screw in anyway just to be safe and I tried a self-tapper but could not get it to bind so it looks as if the lens cover is tapped with a thread but I don't have a screw to fit.

I thought about putting a screw in anyway just to be safe and I tried a self-tapper but could not get it to bind so it looks as if the lens cover is tapped with a thread but I don't have a screw to fit.