1/4-28 UNF threads are popular thread types because they can be connected to both 1/16" and 1/8" OD capillaries with appropriate flat-bottom fittings.
1/8" OD capillaries are usually used for flow rates of several hundrets of milliliters per minute. Above this, 3/16" or 1/4" OD tubing is often used.
To integrate devices with a 1/4-28 UNF thread into 3/16" or 1/4" tubing systems, adapters are required.
The table below gives a recommendation for this.
In any case, make sure that the flow-through equipment is designed for the intended flow rates!
| Flow rate regime | Recommended tubing OD | Small part recommendation to connect to 1/4-28 UNF port |
|---|---|---|
| Up to 100 ml/min | 1/16" | *Fitting A58291 and ferrule A58292-1 |
| Up to 500 ml/min | 1/8" | *Fitting A5829 and ferrule A58294 |
| Up to 3 000 ml/min | 3/16" |
English adapter A7233 + Fitting A142700 |
| Up to 15 000 ml/min | 1/4" |
English adapter A7230 + Fitting A142614 |
*Note: Standard flat-bottom ferrules are made of ETFE, which are used in the low-pressure range (up to approx. 50 bar). Item FZG10 contains a complete set for 1/16" and 1/8" OD capillaries. For highest pressures (up to 172 bar) please use PEEK ferrules instead (set: FZG11).
