what size is lower rad hose

trying fine lower rad hose size for Phillips & Temro 3200003 Block Heater, my truck is 2011 sprinter 2500, and it super cold here been hitting few time -50c at night and about -30c during day. Any help would be great need good into town some time this week.
thanks

intercity1,
According to the MB Compliance Engineering group the P &T 3200003 block heater is suitable for 1 1/2" hose size.
Here's a link to the bulletin:
https://sprinter-source.com/forum/showthread.php?t=43302&highlight=OM-642+block+heater
P&T seems to have a whole series of block heaters to suit different hose sizes and the last number is the hose size
in 1/2" increments.
Hope this helps,
Roger