The bracket on the right is stamped SLATER with (either a R or L) Of the 4 pin style brackets I have found in Canada this is the oldest and second most common. Three pieces of stamped metal rivited together attatched to the crossarm with a flat iron U bolt also marked SLATER; with four pins that accomadate wooden cobs for normal pinhole insulators. The picture clearly shows how the pins bolt to the frame. Two wooden cobs are removed that show the different threading of the pin. I have also found this bracket with the narrower U bolt similar to the other bracket shown.

The bracket on the left is marked R ( and I assume others will be found marked L) Same construction as the first but the pins (carrier pins for CD 128 or 129) are not base threaded but are rivited to the frame. The rivit head is stamped CLM. See [id=155938722] for another view. Out of about 500 of this style bracket that I have, this is the only one with rivited pins.

Picture shows both a R and a L bracket. Each is a mirror image of the other.