Which of the Following PDI Spring Guides & PDI Ezy Hard Piston

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Hi couple more questions please

Which of these Springs Guides should I buy if I'm using this
PDI Ezy Hard Piston for Marui VSR10

I was going to use a 7mm spring guide though I think it might be better if I use a 9mm spring guide but why are there 3 different types of PDi Spring Guide as they all seem to be 9mm

PDI Bore-Up SPRING Guide - VACUUM TYPE (9mm Diameter) for Marui VSR10

PDI Ezy Spring Guide (9mm Diameter Big Bore) for Marui VSR10

PDI Ezy (VACUUM TYPE) Spring guide (9mm Diamter) for Marui VSR10