Yuyuvan Bed Level Springs for 3D Printer Compression Mould Die Springs 8mm Od 20mm Length Light Load Red for 3D Printer Ender 3 Upgrade Cr-10 Cr-10mini Cr-10s S4 S5 Series More Tension Stable 10pcs

I got enough in my package for two printers, and two extruders (if you really wanted the stiffest extruder ever haha) and ive used them on my Alfawise U30 and it stiffened the bed up perfectly. The only slight downside to them is they are slightly shorter than the stock springs, so I found i had to lower my Z end stop ever so slightly. By about 2 or 3 mm so that the bed could be tightened down to the springs to a acceptable tension and not have the hotend floating way over the surface haha. Easy to install, and I really love the performance im getting out of them.

Worked great on my extruder gears. Will be buying more.

A little short but work would prefer them to be a little longer shorter than original springs and only slightly stiffer.