This part is not available separately. I suspect it was the 2nd pair that comes with an osmolator that is only for mounting the optic sensor, they come with 2, one is complete, one only has the mount for the optic sensor. The only spare part is the optic sensor mount and it would be possible to glue a 3150.100 on, but it is not the original clip in part, this was an older part that slides into a mount on the older rails or the comline filters