READ THIS! link below!
To clarify, this is designed to gearboxes without QD spring guides. The tool is useful with some gearboxes that don’t hold other parts in place well in which case you need more hands to hold them in place. Can be used when closing and when opening gearboxes.
Fits most gearboxes but it is compatible with standard v2/3/6/7, and svd gearboxes.
Buy it here:
https://www.shapeways.com/shops/maekiiiairsoft
https://www.shapeways.com/product/UXZQBJULA/spring-guide-holder
Source
Spring guide holder tool for AEG