I bought something like this off Ebay: http://g02.a.alicdn.com/kf/HTB1S5xyLpXXXXcGXXXXq6xXFXXX1/New-Fashion-DC-font-b-12V-b-font-2A-Pull-Type-Linear-font-b-Solenoid-b.jpg Turns out it wasnt as powerfull as i need it to be but it has the right amount of travel and is nearly perfect in size... Notice that the body where the coils are is fairly short. What if i made my own? But MUCH longer body, (theres plenty of room in my aplication LENGTH-wise) will it get more powerfull? Can i make it more powerfull by adding more coil? Turns out i have plenty of coil like the one used in my solenoid, i have plastic pipe similar size and i can CNC the central "plunger" rather easy as well. Or make it different shape etc... The solenoid i have has a metal body, does that affect how strong the solenoid is? The coils are wrapped around a plastic tube, the plunger is rather loose inside it and the tube could be thinner. Will thicker plunger and thinner tube improve the power? Im using a 11.1V lipo battery, something you can find in RC-cars. Increasing voltage/amps IS NOT AN OPTION. So, in simplicity, if i make a solenoid like mine, but longer, can it pull greater load than the original or do i need to do something else as well? The actual aplication itself in simplicity is the solenoid pulling certain object back around ~10mm AGAINST a spring, not very powerfull spring might i add. It pulls the object back, then lets go. It will be controlled via a circuit later but right now just a battery and nut-job holding a red button. I just need a solenoid powerfull enough to overcome the spring. The object needs some force to return to its position so putting in a smaller spring is not an option eighter.