Two-Y

The video shows winding the nylon strings into the 'Four-Wings' and feed them.
Four-Wings is a four-string trimmer head, but a 4.0 mm thick string is used as two-string.

The 2.4 mm (.095') thick nylon string can be wound up to 3.6 m (11.8 ft) with 4 strings.
These High Capacity characteristics ensure that you do not have to shut down the engine to change strings during work, so work continues continuously and seamlessly.

The 4.0 mm (.155') thick nylon string can be wound up to 2.8 m (9.2 ft) with two strings.
※ As a result of the recent test, the string of 4mm can be wound as much as 1.9m in four lines.
The use of thick nylon strings improves cutting capacity and never stops working with strings wrapped around branches or fences.

More Details: http://www.twoytech.com/four_wings/en/