Review on Peeper Keepers: The Ultimate Adjustable Microfiber Screwdriver for Men's Sunglasses & Eyewear Accessories by Tim Kallimanis

Simple and effective, no frills. Stem holders stay securely in place and are flexible enough to slide over a 5/16" wide stem. The adjustable closure feels a bit loose for me, although my prescription glasses stay in place if I put them on or drop them. Around my neck during the day when I don't need to wear them at the time so I got these mounts which are well worth the price and avoid scratching the lenses from carelessly stacking lenses.