This is a replacement electrode probe for the Beverage Doctor PH Meter.
We all know that home brewers are pretty tough on PH Meters.  Putting your electrode/probe directly into hot wort is quite common amongst home brewers.  Doing this can very quicly reduce the life of your probe.
Also the thin glass membrane of a probe can easily be damaged if dropped or mistreated.  As a result we would always recommend that home brewers buy a PH meter where you can purchase the replacement probes separately.
This probe type comes with a small piece of sponge in the cap.  The sponge has already been saturated with PH storage solution (kCl - 3 mol/L).  The storage solution can be purchase separately (Part: KL04183).
Its very important that in order to keep your probe in the best possible condition always keep the end of the probe moist in storage solution.  For the same reason we have designed the probe cap with an water tight o-ring seal so it keeps the solution from drying out in the cap.  This is an essential part of a good quality PH meter design.  If the probe dries out it will also significantly start to reduce the life of the probe and the accuracy of your results.