The first antennas I built used fishing poles from fiberglas as spreaders. 1 year or 3 little DX-peditions later all spreaders were broken. The problem is that fishing poles are to soft and cannot withstand radial forces. The fixing points at the baseplate and the hose clamps which lead the wire elements are the places where the spreader will break.
So I finally came to custom made spreaders made from wounded fiberglas. They are conical to bring the right shape into the antenna. Non conical spreaders try to bend in one point only.
The material is really strong untill today I never had a broken spreader.
Unfortunally this material is very expensive and the pricebuilding component of the antenna. But starting cheap and dirty will drive you to frequent maintenance/replacment and finally to the same or higher costs.
The foto shows my Van standing on the spreader of a 20-10m version.
This mostly explains better how strong the spreaders are than all my words.
Also the new spreaders are not telescopic ones which means they cannot move into each other like telescope fishing poles.
The length of each piece is 1,60m. For the 20m versions each spreaders has 2 elements and for the 40m versions each spreader has 4 elements.