What are sharpie sized curls?

in Hair Type 3
I see this site claim 3B = Sharpie sized curls. What size Sharpie? There's the fat ones and thin ones. I see some claim 3B that look 3C to me. I'd like to help my friend out, but we need clarification.
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Comments
3a, fine, thin, normal porosity, no dye, greying naturally
Devacurl Weightless Waves Low Poo & Conditioner, B'Leave-in and Ultra Defining Gel
Curl Junkie Spiral Lotion in low humidity
Ouidad Advanced Heat & Humidity Gel mixed with UDG for high humidity
at home gelatin PT
Hask Argan Oil Deep Conditioner