Keep in mind that sometimes grades are combined (Select & Better, Second and Better, etc.) or are a mix of two standard grades (No. 1 Common, No. 2 Common, etc.).
Second & Better is a combination of first and second grade wood from a production run, with the second grade being the lowest grade allowed.
Compared to Oak grade rules – First Grade = Select & Btr / Second Grade = #1 Common / Third Grade = #2 Common
This grade is the highest for these species of wood in terms of durability and appearance and is almost entirely free of defects. Variations in the natural color of wood are not considered defects. The following are admitted: small, firm pin knot not exceeding 1/8" in diameter; occasional dark green or black spots or streaks not exceeding 1/4" wide; and small burls.
Expect more wood characteristics and imperfections in machining. These include color variations, streaks, stained sapwood, sound tight knots and slight checks. All defects must readily fill. The following are also permitted: small rough spots; slightly torn edges; small bark streaks; and slight variation in angle of end matching.
All defects are tolerated in this grade, though the wood must lay and give a serviceable floor. There are some limitations: this grade will not admit larger knot holes (.75 to 1"), heart checks and other imperfections that would compromise quality. This grade is rustic in appearance.