Filament width sensor (top) bowden

A very quick and dirty mod of the original (credit to jasonmrc). This reduces the internal friction while the filament is flowing through, while allowing a quick bowden tube connect/disconnect.

Adds:
4mm OD PTFE tube through middle
PC4-M6 thread mounts either side
about 1.5mm height to accomodate the extra tubing & mounts

I have printed successfully with this with TPU/flexi without any real adverse effects, normal caveat of YMMV.

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Post print, I had to ream out the centre hole