The YSL-640 has a continuous taper bell section that improves intonation with even resistance in all registers. The chrome-plated, nickel silver, drawn inner slide is very durable and has a quick, sensitive response. The outer slide is one piece, drawn yellow brass and maintains an accurate diameter throughout its length. This type of construction ensures airtightness, smooth action, exceptional durability, and adds resonance to the sound. Long-lasting nickel-silver tubular braces contribute to the stability of the slide and enhance smooth slide action. Tuning slides are hand lapped to ensure an absolutely perfect fit and seal between the slide parts.

The virtually seamless bell--fused by high-energy laser--allows continuous, even vibration. The unique slide lock design on all Yamaha trombones keeps the slide locked in place and prevents it from accidentally falling. Large, easy-to-hold, nickel-silver bracing guards against possible slide damage if the instrument is dropped and also lessens fatigue while playing. Mouthpipe features a special acoustic design that allows precise intonation and greater blowing control. Large rotor on "F" attachment makes transitions from the Bb to F smoother. The hand-lapped rotary valves provide airtight, light action for quick and smooth valve switching, while the string linkage permits flexible adjustment.
All Yamaha wind instruments come with a limited 5-year warranty.