They are insulators that have a clamp that holds the wire, not tie wire like what national grid uses. NU only now uses vice top insulators on all there primary wire.
The pole in front of my house has two different trpes on it. It has a glossy button looking one like the one above exept white. The other one looks like stacked discs.
Yep those stacked disc are polymer insulators and the button type are glass. Vice tops are polymer. Check out the 250 watt m-250a2 pic in my gallery and you'll see the 15kv vice tops on the pole.