Mechanically-interesting Father's Day Gift Ideas

Keychain
http://www.woodpaperscissorsuk.com/listing/270213765/wooden-cogs-and-gears-keyring

Yot
The YOT is a shiny metal disc (not a UFO!) that holds a US silver dollar coin. The challenge is to remove the coin without power tools! It relies on a fundamental law of physics - can you solve the puzzle and open the YOT? 
http://www.yot.com/theyot.htm

Jewelry

Solid stainless steel ring features real-working gears that turn when you spin the outer gear band. Engraved initials, carbon fiber inlays. Gift box.

http://www.bradfordexchange.com/products/121537001_mens-stainless-steel-gearhead-personalized-ring.html?cm_ven=GPS&cm_cat=Google%7CProductAds&cm_pla=&cm_ite=121537001&gclid=Cj0KEQjwhZm7BRCUyfS6ho2VjOEBEiQAumpGMsC8EtOV2exYGyG3r8Csr6oQ52fLC1Egzur_XAgxYaYaAsXE8P8HAQ