These clamps are for mounting the Semi Flexible Frameless or thin film solar panels that are sold on eBay.  (If the solar panels flexable enought so they can roll up, these clamps will require modification to work with these panels.) 

These clamps include the locking nut and the hard to find T-Bolt mounting bolt for 1/4 opening on rails such as Unirac.  The T-bolt and locking nut are zinc plated to prevent rust.  The mounting brackets are approximately 8 cm long. 

Please note the mounting bracket mount on the rail as shown in the picture.  For mounting of 4 solar panels you will need 4 quantity end clamps and 6 quanity mid clamps. 

Here is an example of the panels these clamps are designed to work with.

http://www.ebay.com/itm/320W-Semi-Flexible-Frameless-Mono-Solar-Panel-24V-320-Watt/282062717127?_trksid=p2050601.c100085.m2372&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D37338%26meid%3Df60994c58b714007b367fe6ea035b202%26pid%3D100085%26rk%3D4%26rkt%3D4%26mehot%3Dpp%26sd%3D121936297318%26clkid%3D8231347948051093462&_qi=RTM2247628