BambooMN Extra Long Draw 39" (100cm) Bamboo Arrow Shafts, 10 or 25pcs - Various Spine Weight Groups EXTRA LONG SPINE: Bundle of 25 39" (100cm) long Bamboo Shafts, 40-45# spine weight HAND STRAIGHTENED BAMBOO: These shafts measure about 7mm in diameter and are perfect for making traditional natural arrows. The "knuckles" of the bamboo stalk have been shaved down and the finished shaft is sanded smooth and laquered. TRY YOUR HAND AT FLETCHING: These are bare shafts with no nocks or fletching for those who enjoy the challenge of fletching their own arrows. STRONG AND DURABLE ARROW SHAFTS: Bamboo is tougher than most hardwoods. Also known as nature's carbon, it is an excellent material for the construction of durable arrows. NATURAL TAPERING: Very slight natural taper makes for arrows that are slightly forward heavy, and very forgiving to shoot. You can usually choose a spine rating 5# higher than you normally shoot. We measure the spine of the middle 26 inches of each shaft. This means that you can fine-tune the spine of your arrows when you cut them to length. Cutting an even amount off of each end will keep the spine rating the same, cutting from the narrow end will result in higher spine, and cutting from the thicker end will result in a lower spine.Always attach the nocks to the thinner end. Our shafts are sold grouped by spine weight in 5lbincrements. Spine is measured by hanging a 2lb weight from the center of a 26-inchsuspended section of shaft and measuring the deflection (AMO method). Less deflection means a higher spine weight. Because of the forgiving nature of slightly tapered natural arrow shafts, you can construct arrows with slightly higher spine than you typically shoot with your bow. Try selecting a spine weight at least 5lbhigher than you normally shoot with normal parallel shafted arrow.