The reel holder is a piece of MDF (10 x 10 x 2cm, or any wood but the heavier the better) having a 9mm hole drilled in the center. A 9mm diameter dowl (10cm long) is fitted and glued into this hole. Over this is pushed a 35mm film can lid (drilled out to say 8mm hole. The reel of wire rests on this and lets it rotate with less friction.
Finally, near to one corner of the wooden block another hole is drilled and a second dowl (9mm x 8cm long) is fitted. This second dowl has a 2mm hole drilled near to the top of the dowl. The end of the wire is threaded through this hole and guides the wire when it is unwinding. This stops the possibility of a loop (or many loops) coming off the top of the reel and starting the seed for a birds nest tangle of wire.