The Featherweight uses the common needle type which goes by several different designations; 15X1, 705, etc. These come in sizes from 8 (smallest) to 19 (largest). The “size” refers to the thickness of the needle, and not the length. All modern household machines, Featherweight included, use the same length needle.
The critical difference between the Featherweight and most other machines is that the NEEDLE IS INSERTED WITH THE FLAT SIDE OF THE NEEDLE TO THE OPERATORS LEFT. (Illustrated above) Unless the needle is inserted correctly the MACHINE WILL NOT SEW. Certainly you must also be sure your needle is not bent or blunted. Better to dispose of a questionable needle than take a chance
Although the Singer “color-coded” needles are suitable, I prefer the Schmetz brand for quality. Any others should be avoided.