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. Keep in mind that, although you can add a QR code now, you do not have to use a QR code. Just set the QR Name to "" to work just like the old version of this thing.
The OpenSCAD file has fairly obvious, commented, parameters that can be set using the Customizer or by manual editing of the file. There are way too many useful combination possible, so no STL files are posted here -- just the OpenSCAD source.
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.
The original version was distributed under the Creative Commons Attribution license. This version is GNU-GPL because the QR code generator it uses is. However, that QR code generator can be removed from the end of the OpenSCAD source without damaging any other functionality.