The Train Line Roundabout Connector. Connect with Roundabout by aligning the small pillar in the middle.

You Probably will need unrestricted nudging via the infinite nudge mod to place these (https://ficsit.app/mod/InfiniteNudge)

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Roundabout Cap (https://satisfactory-calculator.com/en/blueprints/index/details/id/7088/name/Roundabout+Cap+%28TL%29)

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This is Part of the Retrofuturistic Railway Collection

(https://satisfactory-calculator.com/en/blueprints/index/details/id/6512/name/Retrofuturistic+Railway+Collection) If not specific to this part please leave any comments there.