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).