Matthew Jennings wrote in to let us know about his illustration libraries. For £10-15 (USD $16-25) you get a set of fasteners, power connectors, or computer/AV connectors, all in vector format ready to use in illustrations, instruction manuals or parts diagrams. The illustrations show a nice attention to detail and line weight.
Kevin Hulsey offers a similar fastener library (USD $50), with a smaller selection of parts but a greater variety of angles.
Scoop all these up and you’ll never have to fuss with drawing a connector again!
Update: Matthew has added two new libraries. The Fixings library (£15.00) is a collection of 23 common fixings in varying degrees of rotation, and comes complete with placement guides for precise positioning. The Measuring and Marking library (£7.50) contains a variety of measurement tools. Get them here.