I have 2 bikes with trekking bars both with, as you call them, twisty shifters.
and a 3rd on a straight bar also with a grip shifter... all 3 are operating internal gear hubs
all 3 bars are 7/8" tube aka 22.2 mm in common.. a mountain bike bar size..
From your description you might have a low cost bike comprised of low cost component parts....
Where did you buy this bike? what is the rest of the drivetrain?
....
Last edited by fietsbob; 06-09-19 at 11:04 AM.