The hole for the momentary switch is 7mm in diameter. Modify or drill out to accommodate for larger/smaller switch you may purchase.Print with 0.3mm thickness or less. I used 0.3mm and it printed fine. Print with an infill between 15% and 25%. The slide cover location of the main file has integrated supports so remove them prior to installing the slide cover. Installing the switch is a little tricky, but be sure to wire everything first. ALWAYS LAUNCH MODEL ROCKETS IN A SAFE AND OPEN AREA. HAVE FUN.