I made these for my brothers Hot wheels Ecto 1 elite 1/18 scale (I think), it comes with the stretcher but no Proton packs unfortunately, which is a bit of a swizz considering how much they cost.
These are resin casts, I made the original from all sorts of bits, styrene sheet, rubber, q-tip sticks, bits of guitar string, sections of drinking straw, a bit of Sculpey, wire and some rubber tubing....I think that's it.
Painted with acrylics with a couple of tiny blue and red stickers to finish.
They measure approximately 4 x 2.5 cm at the widest parts, I think they're actually a little big for the stretcher and they're a little rough up close but they'll do.
If you don't love Ghostbusters WHY THE HELL NOT??? are you crazy?????