mcmcaster carr is also extremely popular in the hobby drone building market for buying bolts/nuts/fasteners/standoffs to attach circuit boards (ESCs, flight controllers, etc) to carbon fiber plate, and for attaching cnc cut carbon fiber plate piece together to build the whole frame of a small UAV.

people in the film/tv/production industry also use them to buy various fasteners and hardware for rigging lights, microphones, building complex camera systems onto gimbal platforms, etc.