I prefer laser drilled carto's over punched, the holes are uniform and the process doesn't distort the carto body.
You can
buy pre punched or lazer drilled carto's or a carto punch or something that will work as a carto punch from many different places.
Hardware stores carry 1/4" self tapping saddle valve that will work, best to practice on a few old/unusable carto's first, you may have to remove and sharpen the tapping screw to keep body distortion to a minimum. I have replaced this screw with a self tapping metal screw but forgot the size/thread/length used.
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