Use a cap to close off a tube with a ferrule and internal nut already made up. A cap is essentially a piece of hex stock with a zero volume fitting detail machined into it, but with no through-hole.
| Fitting size | Length of nut* | Product No. |
|---|---|---|
| 1/32" | .30" | ZC.5 |
| 1/16" | .43" | ZC1 |
| 1/8" | .57" | ZC2 |
| 1/4" | .70" | ZC4 |
