Can anyone recommend a good focus rail?

Getting back into Macro and just picked up a Nikon 105mm macro D lens.

Want to start using manual focus and wondering if anybody can recommend and good site or has tips as to equipment or methods that work best.  For instance, I have been told a focus rail helps with manual focus macro work....any thoughts? and where might I find a decent one or are there any to stay away from?

thank you.

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w