https://www.dell.com/en-my/work/shop/dell-networking-sfp-transceiver-1000base-t-up-to-100-m/apd/407-bbos/networking

That is probably what you need.  I can verify they do work in the 5248 switch.  Quick note that they only support 1Gb/s, not 100Mb.  So unless you're doing 1gig over that cat-5, this won't work.

Thanks for the reply. 

A Dell engineer finally responded with the part number 4NHHH. Which does not come up in any searches but, apparently can be ordered.

I don't know why they make this so difficult.