On one of the sites, Pyramid in the UK, or the fenda extenda site here, it says this is a adhesive attached part due to the design of the fender.
However, it comes with 4 push type plasitc pop rivits. I did not use those.
The Extenda also has double stick foam tape to hold it in place while drilling holes or glueing.
I would strongly suggest that you remove the fender. It is easy. 2 screws and the brake lines are off, then 4 screws and the fender comes right off.
Then fit the part a number of times until you like the way it fits and looks. Do not peel the tape off yet.
Clean the fender mating surface. I cleaned the plastic with MEK, which is too strong(will melt the plastic), but took the shiny off and mold release, etc. Yeah I was anal. I then took a sharp nail and scratched up the mating surface pretty good to give a better bite for the adhesive.
I used 3M 5200 fast cure. 3m's site says to test on plastics first for suitability, but remember, boats are made of plastic. Fiberglass is known as FRP-Fiberglass re-inforced plastic, or GRP, Glass re-inforced plastic. I know there are different kinds of plastic...
Anyway, after fitting it the way I liked, I peeled off the tape and put a lot of 5200 on the mating surfaces and put it in place. I did use some small clamps to hold it, but the tape did all the work as it turned out.
Notice that when fitting, the extenda will pivot at the tape. Make sure you have it aligned the way you want so it looks like an extension of the fender, following its curve, and isn't pointing at the tire. That left a gap at the front of the mating surface under the fender (the edge farthest from the bottom edge of the fender). I filled that in with the 5200. I have pictures, but as yet still cannot post them. I will send them to you if you want, PM me an email address.
You might want to remove the sticky tape, but that looked like too much work. Also, at first I tried to install the extenda with the fender on the bike. AND, ended up having to remove it with the extenda glued up...
If you leave the tape on, you must use enough adhesive to be above the tape and, enough to fill in the gap at the top of the mating surface if you have one. Use too much and you may have a mess. I actually managed to use just about the right amount, and only have to "caulk" at the gap and around the edges. I had no mess. For once.
After the adhesive sets, re-install the fender, paying attention to the weird little brake line fittings, and you are done--Almost!! Now, re-polish your fender to get your finger prints off of it!!
Having said all that, it was easy, and it is not coming off.
