1/8 male thread x 1/4 compression nut Elbow used commonly in connections to RO membrane housings.
If this fitting in to the drain line, then it may also have a drain line restrictor inside.
The restrictors can be difficult, if not impossible to re-use.
We recommend purchasing the elbow with a restrictor already installed.
Such as part # 44FR125256JF, or # 59JGFR50220.