For those who collect foreign and believe only J. Stolle Niemen has the so called Niemen notch on bottom of crown. This insulator is marked ( H.M.) only on side of crown. The HM stands for Nechaev-Maltsev. Made around 1900 by the Maltsev glass factory near St. Petersburg, Russia. Inner skirt extends to base. Also unusual about this piece is the outer skirt is 9/16 inches thick glass. Very heavy. It is 3 9/16 wide by 5 tall