Struggling with the lower wire ridge on this. It looks more sharp/angular than curved like others I have seen. Also the size of the wire groove is tiny. My phone charger cable fits perfectly with no extra room.

BE matches AM. INSULATOR CO. 156.1 [020] base width 3 1/4, height 4 1/8 {156.1 BOOK DIMENSIONS: WIDTH 3 1/4, HEIGHT 4 3/8}

Jack Kesling distinguishes two styles of the American 156.1, a wide groove and a narrow groove: [id=79721598] [id=79721841]

The groove on mine is much narrower than the groove on his "style 3". I feel the dome shapes on both these fit right into the 156.1 category.