Have a looksee here for what goes inside those end-fedz.
73 de David vk2dmh
Some even use a fixed capacitor soldered across the toroid for QRP work. Then they tune each endfed wire to minimise VSWR. Done once, then no more mucking around. Here I am quoting from the SOTA group in Yahoo Groups:
"I use a T50-43 core, and I fit it into my MTR 3 band, or into a dental floss case (total weight 10 grams) with an RCA male on one end, a 2mm female on the other for my ATS4. In both cases, then, I plug the end of the #28 gauge teflon wire directly into the radio. The built-in internal version, homebrew effort, I can not assert that it is delivering a perfect match, because I don’t actually know if it is or not. The external version in the floss case I know does.
The EFHW wire has mini-traps each weighs in the order of a few grams made using T50-6 cores. This is most important when using #28 wire to minimize stress on the wire. Mine has never broken (yet) even in 50 mph winds.
73 Fred KT5X (WS0TA)"
(Quoted and passed on by David vk2dmh)