Used delrin and threaded rods. There is an aligning tool by JeepinDoug at RCCrawler.com to make task of drilling on the delrin rod, easy. Only thing is the tool works for delrin rods in inches.

4mm steel or stainless threaded rods are much easier and tough. Just cut to desired length then they're all set to accept the rode end.

Traxxas #5347 Jato Rod-ends shorter rod
Traxxas #5525 Jato Rod-Ends longer rod

Then cut aluminum, stainless or carbon tubes to sleeve the thread rod.

These rod-ends are tough enough for the lower links of Large Scale Rigs, as well.