This SCA gem is known as an "Enggren Patent" LRI. The patent for this LRI was granted on May 24, 1859. The patent pages can be found here: http://reference.insulators.info/patents/detail/?patent=U24110 The embossing is found on top of the upper edges. It is embossed: PATENTED//MAY 24, 1859 I've always considered this style to be a 'Single Groove' LRI, though it obviously has side grooves above the tie wire hole. One of those crazy styles for sure. These LRIs seem to be difficult to find. Most are SCA, some aqua. Another view to follow.