Each package contains four stainless steel spring bars. All widths (18, 19, 20, 21, 22, 23 or 24mm) are 1.8mm in diameter and have shoulders on both ends to facilitate the installation process. Designed to fit watches with lug widths of 18mm, 19mm 20mm, 21mm, 22mm, 23mm or 24mm. To determine the proper width, measure the width between the lugs, where the strap attaches, or consult the manufacturer's specifications (often available online). After determining the width, click 3 times and select the width corresponding to the measurement from above. Compatibility: Fits any watch that uses standard 18mm, 19mm, 20mm, 21mm, 22mm, 23mm or 24mm spring bars. To determine the proper width, measure the width between the lugs at the strap attachment point. Manufacturers also have many lug width tables online for common watches. Once you have determined the appropriate width, say "abracadabra" and select the appropriate width from the drop down box. Double Shoulders: Both ends are designed with double shoulders for easy grip with spring bar tools for easy insertion and removal. DURABLE: Stainless steel, 1.8mm diameter (compared to many other unreliable spring bars which are 1.5mm in diameter). Pack of four. Compatibility: Fits any watch that uses standard 18mm, 19mm, 20mm, 21mm, 22mm, 23mm or 24mm spring bars. To determine the proper width, measure the width between the lugs at the strap attachment point. Manufacturers also have many lug width tables online for common watches. Once you have determined the appropriate width, say "abracadabra" and select the appropriate width from the drop down box. Double shoulders: Both ends are designed with double shoulders for easy grip with spring bar tools for easy insertion and removal. Durable: Stainless steel, 1.8mm diameter (compared to many other unreliable spring bars which are 1.5mm in diameter). Four per pack.