Here are some size one telegraph insulators from different factories. Here you can see DBZ (Д.Б.З. - Donetsk bottle factory), Liv. Obsch. (Лив. Общ. - Livengoff partnership of glass works), Maltsovskoe (Мальцовское - Nechaev-Maltsov's glass factories). These are all from pre-1917's epoch. They were classified as 'telegraph' though were more commonly used on low-voltage distribution lines in urban areas.