These knobs are not all interchangeable.Though they look the same from the outside,there are important differences.In the top photo is my 920T in black.Also pictured is the 3 piece LPC990 (below it) and the 931 beside it.
Here are the knobs for each from left to right (LPC-990,920T,931)
The first knob from the 990 is not chromed and is oriented at 90 degrees difference to the 2nd one,the chromed 920T knob.Notice that both have a shaft.The third knob,also chromed,is from the 931 and has no shaft.Further complicating things,The knobs on the standard (non "T" version) 920 are totally different than the ones on these boxes.They are a larger diameter.
The 920T is a nice little box but were manufactured with fake tweeters.Their "decent" sound becomes fantastic with the addition of real tweeters from the standard 920.Though I've never heard a standard 920,I can assume my "T" version with real tweets sounds the same.If so,the 920 must be a fantastic box!