The figure to the right shows an easily constructed Ag/AgCl reference electrode. The body of the electrode is made from 4 mm glass tube. Vycor® porous glass is available in 4 mm diameter rod and serves as the ionicly conducting electrical pathway between the inside of the reference electrode and the bulk of your cell. It has low electrical resistance (under 10 kohm for the common filling solutions) and a modest leak rate. The electrical resistance of the reference electrode 'frit' is an important factor in determining the stability and speed of your potentiostat in actual use. (See the GAMRY and PAR notes mentioned in the resource on potentiostat stability for more information.) The leak rate may be important because of possible contamination of your solution by the reference electrode filling solution and vice versa.
The Vycor® frit (about 1/8" long) is attached to the glass tube by 'heat shrink' Teflon tubing. The heat-shrink tubing should be cut flush with the end of the Vycor frit to prevent trapping any air bubbles. Pre-cut Vycor® frits and heat shrink tubing are available from Gamry, PAR, BAS, and probably other electrochemistry suppliers. The cap is conveniently made out of scrap Teflon or plastic cap or protector made to fit 5/32" OD tubing. It should be snug, but easily removable for replenishing the filling solution.