Frame extenders/clip ons/knock ons - Argh!, please help!

Hi All,

I need to replace a rotten wooden window, and have acquired a used frame to do the job. As the replacement frame is slightly smaller than the existing one I need to make up the gap using a frame extender, but when I went to B&Q I discovered that they have 2 different profiles, but both have the same barcode/product number!

This is the profile of the window I will be installing:

This is the first extender:

And here's the second:


Now, by my way of thinking the second extender is the best - it has a box profile, so is stronger. and it also seems to be a better fit - any thoughts?

My next question is how to attach the extender to the frame - do I just silicon it on, then the frame fixings will pull it all together?

Thanks for any help!

Go for the second option, screw it on with 30mm self tappers. The add-on normally unclips when the drill hits it. Pre-drilling thr frame first will also minimise the add on unclipping

Also, run a bead of silicone along the frame where the add on will be going

Great, - thanks for the advice!