Side by side.

Specification	SD-509-500L SD-509-W 500L Quote
Width	3.200"
Height	0.700"
Flange	0.250"
Material	Rubber
Type	Sponge
Durometer	2A4 (sponge grade)
Colour	Black
Mount	Push On
Bulb position	Side
Core	SD-500L Spring Steel

Spec sheets live on each part's page.