Just a word of Advise on the Helimax Super Start ; I used it to start my 30 and 50 helis ; However , when I used it on my 90 Heli , The hex-shaft that connects to the spinner cup-broke off inspite that the starter started the 90 engine easily . Replaced the shaft ...and re-broke the same way with the 90 heli. It turned out that there is a design Flaw in the shaft - It seems that Helimax has smae starter design as Duratrax Super Start and used the same Hollow Hex shaft for the spinner cup shaft ; however under pressure from torquing the 90 Engine ....BRRRREAKS. I went to a Lathe Shop and made a new steel shaft but non-hollow . costs 12$; That worked well so far. So if you need it for a 90 size engine, Do the modifications I mentioned, otherwise, you will continue to replace shafts with each engine start for 90 engines; works well for smaller engines without modifications with fantastic torque.