Toroidal cores are used in a wide variety of applications such as power input filters, ground- fault interrupters, common- mode filters and in pulse and broadband transformers.

Dimensions
61.00mm Wide
12.70mm Thick
35.55mm Hole

You can use these cores for a range of Balun and Broadband transformer project.
 
The type 31 ferrite is specifically useful as a lower HF band common mode choke. Please see for more details.