Molts are the most reliable method for sexing. At 3" or bigger it is easy with the naked eye. 2-3" is easy, species depending. down to 1" can be done with some digital manipulation with a high res camera. SMaller than that can be done with a microscope.

When it molts, if you can post a pic, I can help you out.
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KJ Vezino
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Missouri Tarantula Enthusiasts Group