Zonefirst PIRR 4Pdt 24V Plug-in Replacement Relay for many older TAT Mark IV V VII VIII XXXI II and MM-2/3 zone control and accessory relay panels.

A 24 Volt AC, Four Pole, Double Throw Relay (4PDT) which is the relay used on the 4PDR RelaySocket, the PlugIn Replacement Relay, Model PIRR. On 
several older electromechanical zone control panels, the PIRR is still used. This relay has been Used on many older TAT zoning tables, the regular relay. The PIRR replaces the Model RMABS. 
In terms of the plastic case of the relay, the easily replaceable relay can look different.The cases may vary in color from being white, clear, solid red and red see-thru, however the basic relay is the same. The PIRR is commonly referred to as a Form C relay. The cases may vary in color from being white, clear, solid red and red see-thru, however the basic relay is the same. The PIRR is commonly referred to as a Form C relay.

To change the relay, just un-plug the old one and plug-in the new one.