To determine which size clamp you need, assemble your parts as close to how they will be fitted in the vehicle. Then, measure the outer diameter (OD) of all pieces. If you cannot assemble the parts, you can measure the OD of the hose or pipe and add the thickness of any external couplers. For applications where the clamped hose or pipe slips over a barb, the OD is the only measurement you need to know. You should find a clamp whose clamping range covers this size. Ideally, you should choose a clamp where the size you need falls somewhere in the middle of the clamping range, as a clamp's holding force is lower closer to its minimum or maximum diameter.
Package details:
15 Pcs ------- 6.0-7.0mm (0.24-0.28 inch)
15 Pcs ------- 7.0-8.7mm (0.28-0.34 inch)
12pcs ------- 8.8-10.5mm (0.35-0.41 inch)
10pcs ------- 10.3-12.8mm (0.41-0.5 inch)
10pcs ------- 12.8-15.3mm (0.5-0.6 inch)
10pcs ------- 15.3-18.5mm (0.6-0.73 inch)
10pcs ------- 17.8-21.0mm (0.7-0.83 inch)
10pcs ------- 19.4-22.6mm (0.76-0.89 inch)