Recently we replaced some of the rotten and cracked true size 4 in x 6 in. posts under the house in crawlspace. The old posts were resting on concrete pads 24 in. x 24 in. and supporting a true size beam 4 in x 8 in.

The lumber we used is [4 in. x 6 in. x 8 ft. Pressure-Treated Landscape Timber](https://www.homedepot.com/p/4-in-x-6-in-x-8-ft-Pressure-Treated-Landscape-Timber-559000104060800/100043950) , since we couldn't find any true size to match the old one. This lumber is rated as #3 grade but does not have any knots or cracks and labeled as not being used for structural purposes. 

Should I be concerned about its strengths? I presume that is Douglas Fir.