TABLE OF CONTENTS 
| W | = | width of lock (folded edge) |
| G | = | width of grooved seam |
| L | = | width locking strip |
| P | = | width of paned down seam |
| K | = | width of knocked up seam |
| T | = | thickness of metal |
| Type of joint | Approximate allowance |
|---|---|
| Grooved seam | Total allowance = 3G ? 4 T shared:
where joint centre position is critical. |
| Double grooved seam | Add W T to the edge of each blank to be joined. Allowance for capping strip = 4 W + 4 T, where L = 2 W + 4 T. |
| Paned down seam | Add W to the single edge 3. Add 2 W + T to the double edge 4. P = 2 W + 2 T. |
| Knocked up joint | Add W to the single edge 5. Add 2 W + T to the double edge 6. K = 2 W + 3 T. |
