FJC 6820 Conversion Kit

That adaptor is so you can use the R134a manifold set that you already have. I'd recommend these instead. https://www.amazon.com/FJC-6820-Conversion-Kit/dp/B00CBB9D04/ref=cm_cr_arp_d_product_top?ie=UTF8

You don't have to make anything, you can buy R1234YF couplers that will fit standard HVAC manifolds. https://www.amazon.com/FJC-6820-Conversion-Kit/dp/B00CBB9D04/ref=cm_cr_arp_d_product_top?ie=UTF8