This is my first attempt at designing a heater block for the mk5/6 extruders that will accept a .25"x1" cartridge heater.There is also a spot on there for a 250c thermal switch (Microtherm PN 55H12T944). The thermoswitch is rather large so it may be better to use a thermodisc part such as PN G4A01240C which is much smaller.I don't have my cartridge heaters yet. I'm just uploading this in case people want to give me their input on the design.