2) MagFilter threaded adapter which is meant for compact cameras with certain sized lenses. It comes with two adhesive metal rings to fix onto the lens, and a small carry pouch. The metal ring once stuck onto the lens will allow the MagFilter adapter to stick to the lens via magnetism, and hence allow the use of a filter on a lens which does not have filter threads.
The MagFilter threaded adapter ring I bought was for 52mm filters, although they also come in 55 and 58mm. The adhesive metal ring for these adapters has dimensions: 37mm outer diameter and 32mm inner diameter. BTW, the MagFilter threaded adapter also comes in 49mm. This would have been perfect for me, but for the fact that it uses a much smaller adhesive metal ring (31.9mm outer and 27.8mm inner diameter), hence no good for me. You will need to check whether these ring dimensions will fit the lens you own – it does work on some of my lenses (I will talk about these lenses in another post).
I bought my MagFilter threaded adapter on eBay for £25.99. They do work, but the magnetic force is not strong enough to prevent the filter from falling off if it accidentally knocked against something; hence I have a string attached to it as a precaution. But for the price and for those smaller lenses, this could be a viable solution. Score 6/10 (for low price and use with small lenses)