shouldn't be hard to figure this out for yourself. find a small non-distinguished round spring, and some kind of plunger.
P.S., if you need an emergency spring assortment, those crappy hex key sets on a ring, with the wire wrapped around to hold them on, work. just pull to expand them and make a compression spring. good range of diameters, way better than most spring assortments. that trick has saved my ass a number of times.
(apologies to the cognoscenti, now ive done it, let our secret out!

)