Although the customizer parameters are well commented, please see the Instructable, http://www.instructables.com/id/3D-Printed-Screw-In-Front-Lenscaps/ , I wrote giving the details -- especially about sizing the lenscap.
The OpenSCAD file has fairly obvious parameters that can be set using the Customizer or by manual editing of the file. You will need to have the Write.scad library in order to create the labels using stand-alone OpenSCAD to make STL files.
Pick a plastic that has a neutral color so you can use the lenscap as a color reference. The Rosewill Grey PLA used here is quite close to a neutral gray. White or gray PLA, or clear T-Glase, are what I'd recommend.
It's a straightforward and fast print, although it does have tight precision constraints on the thread diameter and pitch. PLA tends to work better than ABS because ABS doesn't hold dimensions as well over a large diameter; I also find using no more that 40% fill gives less distortion of the parts as they cool. The 0.75mm pitch typical of filter screw threads is really much too fine to be printing on typical consumer-level printers, but this uses a slightly tweaked metric-compatible thread design that prints easily in PLA on my MakerGear M2 even with 0.25mm extrusion. The printed thread is quite shallow, but it's more than sufficient to hold the cap in.