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This is a Female adapter. It allows two Male ends of my other modular lightsaber parts to fit together. This part, like my other modular lightsaber parts, is sized to accept a small flashlight inside like the one found here: https://www.harborfreight.com/3-12-in-Mini-Flashlight-69111.html
This part allows for double-ended lightsabers or pieces to be attached in unique orientations.