4 Pin bracket found in Canada in great numbers, this is the commonest bracket here. Marked SLATER (R or L) it has carrier pins for the CD 128 or 129 insulators that bolt to the frame.. One piece of flat metal bent to shape attatched to the crossarm with 2 long bolts.

The bracket on the left is marked with R but is different in that it has a little extra flange to the outside to extend it's width and accomodate an extra bolt hole. Out of about 500 of this style bracket I have found 2 with this feature.