Here is a working Western Electric telephone U type receiver element for 500 series phones. Originally these were made for G type handsets and they will work well for that purpose. These also work well for all old telephone projects. You will receive a U2 U1 or U3 element that works
You can easily substitute this Utype element with most other old telephone elements to achieve better clearer hearing. You can put them in 706 A candlestick receivers and others. Ive seen them used in many antique telephone handsets such as type 38 and they provide a more clear reception.
They work well because there are 2 teminals and on most old phones there are 2 wires with spade connectors.