The 1N6135A: The 152 V minimum breakdown voltage and 218.4 V maximum clamping at 2.3 A peak pulse current define the protection window: any transient that drives the line above 218.4 V gets clamped, but the diode starts conducting leakage well before that — the 121.6 V reverse standoff is the continuous DC voltage the part can sit across without significant current draw. The 500 W peak pulse power is rated for a through-hole axial TVS.
Package is Bulk, through-hole axial. The B Axial case is the common leaded format that fits existing PCB layouts from the 1N6135 series. No surface-mount variant is listed — if your board uses an SMD TVS, this is not a direct footprint swap.
This is a single bidirectional channel, meaning it clamps transients of either polarity with a single device.