Weight: Each piece in your image is 0.5 kg (approx. 1.1 lbs).
Design: They are typically made of soft neoprene or polyester and feature an adjustable Velcro strap and a metal D-ring for a secure fit around the wrist or ankle.
Usage: These are often used for:
Lower body workouts (leg lifts, lunges).
Adding intensity to cardio (walking, running).
Physical therapy and rehabilitation exercises.