1 Interchangeable needle kits are exactly what they sound like--a set of knitting needle tips, and a set of cords of varying length that can attach and detach from the tips to create many different combinations of needle sizes and cord lengths.
Poor circulation (blood flow) can make your foot less able to fight infection and to heal. Diabetes causes blood vessels of the foot and leg to narrow and harden. You can control some of the things that cause poor blood flow. Don't smoke; smoking makes arteries harden faster.
Though this sensation is not uncommon in people with diabetes, hot or burning feet can have many other causes. Since your friend says his feet feel very hot from time to time, but not all the time, he and his doctor should rule out other causes.