A list of objects with something in common

Pocketknife
Angle grinder (cut off disk)
Angle grinder (sparks)
Lathe gear teeth
Welding slag
Oven
Screwdriver
Pencil tip
Suturing needle
Soldering iron
Brother's fingernail
Hacksaw
Tree branch
Bicycle handlebar
Weed-wacker engine
Garden hose fastener
Gravel
Scalpel
Pavement
Glass