Since CTC 3D printers are essentially clones of FlashForge Creators / Makerbot Replicators, but lack the filament guide on the back, I made one myself. Doesn't require any screws, CTCs and FlashForge Creators should already have holes at just the right place. It's clearly not as useful as some of the other filament guides on here but I've yet to see one you can just clip into the holes. It works well enough though. Make sure to print at a high enough quality, otherwise you'll curse yourself when trying to make the clips fit.