To replace the aluminium lens holder and allows the use of the lens protectors from gopro. Having tested the fit, this works well. The larger model would require the lens protector to be glued into the tarot holder using silicone as this is removable. I will post a working picture once I have sorted my skipping issue! Just seen this http://www.thingiverse.com/thing:255967 from Clough42, nice design for the same thing. I did try and find any on here before, but maybe that was before Feb 22nd! Anyways his design is smaller and lighter, but i feel this design, being bigger, allows you to fix the lens protector too, as i know they are only a push fit, and in the event of a crash, the lens protector could fall off?... thats my opinion, but check it out too! link above.