Just broke the rain guard on a friend's brand new Nikon Monarch 10x42. I would like to replace them with an Opticron rain guard, which look as good as any. Their size range is... 0 - 37mm, 0 - 43mm, 0 - 45.5mm. Presume that 43mm is the size I need, but thought it best check first as the only rain guard I've bought was a universal one.