Nut and bolt sizers are a handy way to figure out the size of ratchet or socket wrench you need for a big project. They're not terribly expensive, but if you'd prefer to build your own for even cheaper, then Instructables user 92greenyj has put together a guide to make your own.
If you're anything like me your typical workflow with wrenches goes something like this: eyeball the size, grab the wrong sized bolt, curse, grab another wrong sized bolt, curse again and then finally find the right size. The nut and bolt sizer helps alleviate this a little. All you need is a sheet of plexiglass, some glue, a label maker and a few extra nuts and bolts. Simply glue the bolts to the plexiglass, label them, and you're done. It's simple, but incredibly handy to have around the house. Head over to Instructables for a full guide.
DIY Nut and Bolt Sizer [Instructables]