Surplus antenna factory parts. This unique spring permits cable up to 1/4" thick to pass through it. No other spring will do this. Custom designed for high quality antennas such as satellite radio and cellular trucker mirror antennas which have the cable inside the mast tube. Below are the specs for this one. There are 2 others listed in this store, The standard and the large.

4.42" long 3/8-24 Thread male 1/2" long  and female threads 3/4" deep
1/4" pass through celar path
Round end caps. 0.164" end cap thickness
6.3mm (1/4") stainless steel wire 16-1/2 turns
1-3/8" diameter expands to 2" mid point diameter
weight 21 oz (1Lb 5 oz)