Simple reduction to a home smokebox.
For fan 4020 on water pipe with 3/4 thread.

https://www.aliexpress.com/item/32809789302.html?aff_fcid=9d7a97391ef448e4a943cbcff86a0080-1704636700921-08612-_rQ7Tft&aff_fsk=_rQ7Tft&aff_platform=link-c-tool&sk=_rQ7Tft&aff_trace_key=9d7a97391ef448e4a943cbcff86a0080-1704636700921-08612-_rQ7Tft&terminal_id=337145c329cf4344a4e9c805f3d39def&afSmartRedirect=y

Inner hole 11.8 mm for a 12 mm tube, just heat it up.

The connection requires:

3x M3x20mm screw

3x M3 nuts

3x washer M3

Aluminum tape can be used for perfect sealing, but it also works without it.