WRS Caldwell Series 300 Block & Tackle Window Balance – 5/8″ Channel, 30″ Length, Stamp 29-9 (35-38

Bring your windows back to smooth, reliable operation with the proven performance of the WRS Caldwell Series 300. The WRS Caldwell Series 300 is a professional-grade replacement balance designed for non-tilt, side-load window systems. Using a precision spring-and-pulley mechanism, it counterbalances your window sash for smooth, controlled lifting and secure closing. Built with a 5/8″ galvanized steel channel, this balance delivers lasting strength, corrosion resistance, and dependable performance in both residential and commercial settings. Compatible with most vinyl and aluminum single- or double-hung non-tilt windows, the Series 300 is available in lengths from 8″ to 49″ and supports sash weights from 3 to 44 lbs. Each balance is sold individually and comes pre-assembled with top and bottom guides attached, ready for quick, accurate installation using standard tools. Selection Guide: Measure the metal channel length only (do not include plastic ends) Confirm 5/8″ channel depth from the spring opening to the back of the balance. Match the stamped number to your sash weight (e.g., “07-1” = 8″ length / 3–5 lbs). Replace both balances in the same window for best results.

Important Notes: The length of the balance will always be one digit higher than the stamp number on the channel. Balances 20″ or longer may require special handling due to size. If your balance does not measure an exact length, contact WRS for assistance before ordering. Accessories and hardware are sold separately.

From single home repairs to large property maintenance, the WRS Caldwell Series 300 combines durability, precision, and ease of installation—restoring window performance and reliability for years to come.
ENGINEERED FOR NON-TILT WINDOWS – Designed for side-load, non-tilt window systems with a standard 5/8″ metal channel, commonly used in vinyl and aluminum single- or double-hung frames. This balance measures 30″ inches in length and supports 35-38 lbs sashes. Each balance arrives pre-assembled with top and bottom guides attached, so installation is fast and frustration-free—no special tools required.
AVAILABLE IN LENGTHS FROM 8″ TO 49″ (3 TO 44 LB RANGE) – The Series 300 fits nearly all non-tilt window sizes, from light residential sashes to heavy commercial frames. Covers a complete range of lengths and weight ratings for versatile use. Each balance is precision-tested for smooth, reliable performance and long-term durability. Sold individually; accessories and hardware not included. Contact WRS if your exact size isn’t listed.
SMOOTH, SAFE & SECURE OPERATION – The Series 300’s precision pulley and spring system balances the sash to prevent slamming or sticking, keeping windows steady at any height. Designed for quiet, reliable performance in homes, schools, and offices where safety and ease of use matter every day.
HEAVY-DUTY GALVANIZED STEEL CONSTRUCTION – Crafted from high-strength galvanized steel for long-term durability and corrosion resistance. Precision pulleys and springs maintain smooth lift through thousands of cycles, ensuring reliable performance for years of daily use. Built tough for pros yet simple enough for DIY installation.
TRUSTED SINCE 1989 – WRS Window Repair Systems has over 30 years of experience supplying reliable, high-quality hardware. Trusted nationwide by homeowners, contractors, schools, and property managers for dependable repairs and long-lasting performance.