The SA15A: It is a single unidirectional channel in a through-hole DO-15 axial package — the same footprint as a standard 1N series rectifier, so it slots into existing board layouts without a pad revision. At 16.7 V minimum breakdown, it starts conducting just above the 15 V standoff, clamping the surge to 24.4 V maximum at 20.6 A (10/1000 µs waveform). The 500 W rating means it handles a single 500 W pulse of that shape; repetitive surges need derating per the datasheet pulse-curve.
onsemi lists the SA15A as Obsolete. A new design should migrate to an active SMD TVS in the same voltage class, such as onsemi's SMBJ15A (SMB package) or SMCJ15A (SMC package), which require a board layout change.
Package and rework note
DO-15 axial leads are hand-solderable and rework-friendly — the through-hole body handles a soldering iron or hot-air station without thermal damage to the die. The lead bend and cut length must match the original board hole spacing; axial parts are polarity-sensitive, with the cathode band marking the unidirectional orientation.