Which Rails to get for PowerEdge R240?

Hi,

Last month I ordered a PowerEdge R240 rack server (without rails). However, when working on installing my server at the institute computing center, I was notified that I am required to bring my own rails for the server. In order to get the correct rails, I did a a quick search on the topic and found that I should purchase the A12 rails for my server (source: Rail Installation Guide at https://www.dell.com/support/home/en-us/product-support/product/poweredge-r240/docs). However, I also found another piece of contradicting info provided on "DellEMC Enterprise Systems Rail Sizing and Rack Compatibility Matrix" (at https://i.dell.com/sites/csdocuments/Business_solutions_engineering-Docs_Documents/en/rail-rack-matrix.pdf), which showed that R240 only works with A4 rails. Therefore, just want to ask if anyone knows which rails is the right one?