50mm x 100mm timber non-existent?

[Sprogginz]

I need to replace the lower parts of a garage door frame due to rot.
The frame is 50mm x 100mm but the closet size comes in at 47mm x 100mm.
To line up the outer sides of the new frame with the old one, what is normally used that's 3mm to make up for the shortfall?
I have a bag of plastic packers, would they do or is there an accepted method?

Also, out of curiosity, why do some sellers actually advertise some timber as 50mm x 100mm but then tell you the finished size is say 47mm x 89mm in the description?

Thanks very much.

 

[big-all]

the actual repair will depend on the actual construction and iff the wood is on the face
you are buying rough sawn timber so if your lucky sanding will take a further 3-5mm off
try an actual wood yard where they may be able to convert timber to the size you need but at about twice the price

 

[phatboy]

With a new blade in a circular saw, buy a 75x125 or similar. Ripping it down is a 10 minute job max.

Over-size by 2mm if appearance is important, and then power plane it down.

 

[DiyNutJob]

Line up the visible side, then hide the wall side with sealant bead. Shim it with plastic or wood as necessary.

 

[big-all]

With a new blade in a circular saw, buy a 75x125 or similar. Ripping it down is a 10 minute job max.

Over-size by 2mm if appearance is important, and then power plane it down.

yes exactly what i would do but with 72 or 96 tooth blade on my dw 742 as a table saw
and rather naughty flip work/mateial without crown guard or riving knife in place so a light sand gives a great finnish or fewer teeth 1-1.5mm bigger and sanded to size