One of the last things I needed to install was a masthead wind indicator. I didn't like the wind indicators on the shrouds. I needed a small one so it wouldn't run into the line for the gaff boom. But I forgot about the masthead light...luckily it just fit with about 1/8th inch clearance!
Rob
(http://i1061.photobucket.com/albums/t476/rbh1515/Mobile%20Uploads/2016-03/7609187E-AE6F-4CAB-89D5-0E5EC57BF943_zpsw84wkc4p.jpg) (http://s1061.photobucket.com/user/rbh1515/media/Mobile%20Uploads/2016-03/7609187E-AE6F-4CAB-89D5-0E5EC57BF943_zpsw84wkc4p.jpg.html)
Looks good. I actually installed mine on top of the masthead light. There was plenty of space between the top of the cover and the light bulb for a nut.
Don't think I could side mount this one into the masthead light.