This part was designed to make DIY all metal hotend for 1.75mm filament. Entrance hole diameter is 2mm. Mount has similar to J-Head groove mount dimensions, it is internally threaded M6x1.
Please see supplied drawing for dimensions and idea how it can be used.
Other parts for DIY hotend, such as 26mm long stainless barrel (also called thermal barrier), heatsink, heater block and nozzle can be purchased in our ebay store.