These Plug Eight handcuffs are an absolutely excellent reproduction of the original Victorian product. They weigh 480 grams. The ingenuity of this design is breathtaking. The 'plug' consists of a small grub screw which is unfastened using the flat head screwdriver one end of the key. The other end of the key is screwed into the barrel. When the first thread finishes you then engage the driver into a further nut which engages with the exterior pin securing the handcuffs closed. You then back out of the barrel by 'reversing' out and replace the plug to completely seal up the barrel. Get out of that one you Artists of Escape! Internal circumference 19-20 cms