V3 has rounded edges for a better feel in your pocket and one handed use. V5 is flat on both sides for easy printing and safer use via a table. V5 is set as pallet. If your printer is accurate. Print V5 with no screw along with the V3 screw. V3 is an unmodified screw and is a more solid option for cutting 3mm filament. Adults...Slide the razor blade into the back of the upper part with pliers. Gloves are recommended. Then install the lower unit and screw. A USA quarter will fit into the slot. The screw is a bit undersized and self threading. Apply 3 drops of oil on to the screw, Then work the screw back and forth until it screws down all the way. The notch of the screw will be horizontal and aligned with the cutter. Make sure the screw/hinge is tight enough that it wont open in your pocket. If your printer is accurate with low strings, the oil may not be needed. Oil is generally needed if printing in PETG due to the stringy nature of the material. Or print the screw out of an alternate material to prevent galling. Everything is scaled in inch with proper gaps for FDM printers. This item has been tested thoroughly before it was made public. The metal screw (1/2"-13x1" Flat Head) can be found here. http://www.mcmaster.com/#90275a712/=w0d5w8. I've printed many of these in PLA, ABS, AND PETG with 10%-20% infill and supports. The example shown is Green Glow In the Dark ABS. .2mm layer. 240 C Extruder , (hovers at 237) 90 C Platform First Layer 80 C Platform Remaining Layers ABS Slurry on a 3/8" Borosilicate glass plate Always use pliers for blade replacement. Keep out of reach of children. Possible choking hazard. If this is ever made as an injection molded item.. Send me a case of them so I never have to buy or print one again. You may sell the 3d printed version. Enjoy. Send me a comment if you love this cutter as much as I do.