Here is a nice Pyrex glass radio antenna (strain) insulator.

Embossed Pyrex / Made in U.S.A. on front. E4 / Pat 1700066 on the back. Crystal clear. 7.38" long, 1.875" diameter. Factory ground on both ends, a few flea bites and rough spots are all that need mentioning. $10 US plus shipping from Canada. I take PayPal.