OurWorkbench.....The website gave a listing of machines the DBx1 sewing machine needle will fit. The Janome 1600P is one of them. I'll give them a try and if I don't like them I'll offer them up for sale.
As to the round or flat shank...all my machines use a needle that is round on front and flat to the rear. I've noticed needles on Amazon that were flat on both sides, and not listed for use in my machines.

Do you have a link?
Do you have a link? ETA: I still want to see these.
Janey - Neat people never make the exciting discoveries I do.
Not affiliated with off-site link(s)

ETA - I think I may have found a site that lists DBx1 fitting for a Janome 1600P-DB which is a different machine as seen at https://www.sewingmachinesplus.com/j...db-special.php versus what I believe you have which is a Janome 1600P-QC as seen at https://www.janome.com/machines/sewing/1600p-qc/

Thanks for the advice, Pam! I do have a Bernina 830 Record. 40 years old. That machine has lived through a lot of history!

If I remember right (going off memory because I no longer have the machine) the Janome 1600 DB took round head needles, and the 1600 QC took flat head needles. I had the DB and it was kind of a pain to find the round needles.

[QUOTE=Peckish;8576177]I agree with the recommendation of using a size 16 or 18 for quilting. It has nothing to do with speed, and there is absolutely no reason why you shouldn't use that size on a DSM.

I was told to use only the High Speed HLx5 needles because they were less apt to break with the high speed. But if you don't go high speed I guess you wouldn't have to worry about it. I do a lot of straight line high speed stitching and don't want to chance a piece of a shattered needle flying out to hit me in the face or eye when I'm zipping along. The high speed needles are recommended in my manual as well. Safety first!

This is what I use: HLx5 90/14 highspeed Schmetz Needles