fit correctly and stopped the fans cooling the block setting off the runaway thermals alarm. but one thing the hot end does sway in temperature to a greater degree now than with the original sock the variance is about an extra +-/3 degrees from original this does in fact tip just below the Filaments best use temps the upward swing is not as likely to exceed the top recommended example: rec 190-220 pla running at 200 hot end swings 192-208 instead of 195-205 the sock should be thermally insulating the hot end so the end stays pretty stable. I have not seen that with these.