I have made reel spacers using black 35mm film canisters, its easy, holds the single reel at the bottom well, and its one less reel to wash if you do not have those neat clips.
Originally Posted by MattKing
To make, all you have to do is take a old canister, black preferably, (but honestly the clear ones don't match as well lol), stick one reel on the center light blocking column, put the canister on top of the reel, against the column, and use the top of the column as a guide to score the can with a knife. then take off the can and use your knife to cut along the score line, and be sure to remove and sharp surfaces or hanging plastic burrs either with the knife, or by sanding lightly.
You will end up with a open ended tube that you can put on between the bottom reel, and the top of the locking film developing canister, which effectively locks the bottom reel against sliding up. Works well for medium format as well with a smaller spacer.
I have included pics to make this clearer.