The arrow-length rule vs What an arrow spine number means: specs compared
Updated 05 September 2026.
8
specs differ
The arrow-length rule and What an arrow spine number means differ on 8 specs: draw length, arrow length, effect on spine, why it matters, what it measures, reading the number.
| Spec | The arrow-length rule | What an arrow spine number means |
|---|---|---|
| Draw length | Measured from the nock groove to the front of the bow handle at full draw | |
| Arrow length | Cut about 1 to 2 inches longer than draw length so the broadhead clears the bow shelf | A longer arrow flexes more, so it needs a stiffer spine |
| Effect on spine | A longer cut flexes more, so it needs a stiffer spine | |
| Why it matters | Cutting too short risks drawing the broadhead onto the hand; leaving it long weakens dynamic spine | |
| What it measures | How far a shaft deflects, in thousandths of an inch, under a 1.94 lb weight hung at the centre of a 28 inch span | |
| Reading the number | A 340 spine deflects 0.340 in and is stiffer; a 500 spine deflects 0.500 in and is weaker | |
| Draw weight | Higher draw weight needs a stiffer (lower-number) spine | |
| Point weight | A heavier point weakens dynamic spine; adjust one spine group per 25 grains of point-weight change |
Questions and answers
How do The arrow-length rule and What an arrow spine number means compare?
The arrow-length rule and What an arrow spine number means differ on 8 specs: draw length, arrow length, effect on spine, why it matters, what it measures, reading the number.