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They are fine and smooth in action too.
There are some much more expensive helical focuser that do have an extra fine additional control, but these are not common. Much like the geared crayford focusers.
I love helical focusers! The are low profile making them a great space saver. In ATM DIY visual scopes they mean you can have the focal plane of the scope closer to the tube allowing for the use of a smaller secondary mirror, meaning MORE LIGHT and better contrast. I'll be using a 2" helical focuser in a travel scope project I'm on.
PS, had to correct some things after re-reading OP.
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