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This is CC licensed, not open source. Neither is the current version which you can find here: https://www.thingiverse.com/thing:1062085

For just making your own GuerillaBeam adapters I recommend remixing this open source part https://www.thingiverse.com/thing:863055
If you want the full Inventor sources (1..6 GB) instead - make me an offer ;-)

GuerillaBeam SLR lens adapters
GuerillaBeam parametric extension tube