Yes, the 1-5941 nozzle will work on the wand for the 21210 sprayer. The flow rate on the 1-5941 is .5 GPM verses the .4 GPM on the nozzle that comes standard on that sprayer. If you're looking for a low flow rate, we would recommend either the .1 GPM fan (1-5915) or the .2 GPM (1-5933).
The Chapin Brass Fan Tip 1/4-inch .5 GPM Female - (Part# 1-5941) will not work for the battery powered backpack sprayer Model#63985. We recommend that you use the 6-8096 Flat Fan Tip this one will increase the flow a bit.