Clecos are a great tool to have around and they come in various sizes lengths. Clecos are used as temp fasteners during sheet metal assembly. They will also work with plasics if your a little more careful. They are used heavily in the aviation industry. It is not uncommon to us 100+ when performing aircraft skin installations/replacements. The most common size diameters are 3/32, 1/8, 5/32 and 1/4 inch and the come in various grip lengths. Some are spring loaded that require cleco pliers to be used and others use a nut or wing nut to tighten them. Thay also offer verious sizes of cleco clamps that can be handy. here are two companies that sell them.
http://browntool.com/
http://www.aircraft-tool.com/shop/main.aspx