A matching necklace pair is two halves of one object. Worn apart they are two pendants; worn together they complete a shape. That is the entire idea, and it is why the mechanism matters more than the decoration.
Three mechanisms
Interlocking — Two shapes that physically link — the "Roman Time" and "Together" interlocking circles.
Magnetic — Two pendants that pull together and sit flush when brought close — "Love Magnetic".
Continuous loop — The Mobius designs — "Connected" and "Unconditional Love" — a single surface with no inside or outside.
Beyond those, the "Infinite Time Lock", "Our Commitment", "Time Together", "Promise Hearts", "Light Year" and "FALL IN LOVE" designs each pair in their own way; the product page shows how.
Most designs here carry a style or colour option so the two halves can be ordered differently — one in each finish, if the two wearers do not wear the same metal.
Material
Every piece is sterling silver, several set with cubic zirconia and one with blue zircon. Solid metal rather than plated, which matters for a pair worn continuously — both halves age at the same rate and can be polished back together.