For an overview on creating, visualizing, and simulating mechanical constraints, including RodConstraint, see Mechanical Constraints. Also see Roblox Units to understand how Roblox units compare to metric units.
A RodConstraint keeps two attachments separated by its defined Length. By default, both attachments can rotate freely, although you can enable limits to restrict rotational tilt.
Limits
You can limit rotation of the attachments within a cone, independently of each other, by enabling the LimitsEnabled property and setting LimitAngle0 and LimitAngle1 respectively.