This J-Head Dual filament can be used for both 1.75mm and 3.00mm filament. To change it for the 3.00mm filament you will unscrew the hollow lock screw and remove the inner 1.75mm PTFE tubing. Please see the picture of the mounting.

The J-Head with bowden tube is only for 1.75mm filament. The PTFE bowden tube is 90cm long and with 2pcs fittings.

This hot-end is a combination of ideas from other nozzle designs combined with a goal to reduce the number of custom machined parts to a bare minimum. The J-Head Mk-V has been proven to print reliably with both ABS and PLA. (PLA will require a small fan to provide air-flow through the cooling vents milled in the sides of the nozzle holder.)

This hot-end easily interfaces with the most popular RepRap extruders, including Wade's Extuder, Greg Frost's Hinged Accessible Extruder, etc.

Advantages

Internally, the filament path is identical to that of an already proven design.
The design is simple as the number of custom machined parts is kept to a minimum.
If necessary, the PTFE liner can be replaced by using an off-the-shelf piece of PTFE tubing.
The PTFE is not stressed nor used to provide support. This reduces a point of failure that is part of other designs.
A heater cartridge is used as a heater. There is no need to wrap nichrome wire or to bake a heater core.
Heat transmission is improved as there is no thermal junction where a separate heater screws onto the nozzle.
The weight is very low, making it possible to print very fast.
Included

Fully assembled J-Head MK-V Hot-End
PTFE tubing for 1.75mm filament
PTFE tubing for 3.00mm filament (not the bowden version)
Fittings for Bowden tube 2 pcs (only the bowden version)
12V/40W heater cartridge
Thermistor 100k
Hollow-lock socket set screw (not the bowden version)
PTFE insulation for thermistor
20 AWG high temperature wire
Thermistor & PID settings

The thermistor is a 100k @ 25 Deg.C type B57550G, it has a B25/100 (beta) value of 4092, for more info see the datasheet.

If you are compiling Marlin yourself we recommend setting the corresponding TEMP_SENSOR_ value to 1
The standard PID setting for J-head in Marlin will in most cases do just fine (Kp 10.4, Ki 0.5 and Kd 55)
If you want to find the excact values for your setup (machine must be up and running via USB cable) you may manually enter M303 S200 in a terminal window eg. Pronterface. (you may substitute 200 with you preferred printing temperature) The extruder will then cycle temperature a couple of times and when finished Marlin will return the recommended Kp, Ki and Kd values to the terminal.

For additional info, see PID tuning or just google for "PID reprap"

Please note a used HotEnd can't be returned or refunded.