Standard Lamp Thread Sizes
Lamp Thread Sizes: are mostly standardized. It is imperative to know the thread size when replacing any antique lamp parts. List of common lamp threads and there uses provides a quick reference.
8-32 - 5/32" outside diameter, used as holder screws with some glass shades.
1/4-20 - 9/16" outside diameter
1/4-27 - 7/32" outside diameter, used on harp posts & most lamp finials.
1/8 IP-27 - 3/8" outside diameter, very common thread used on table lamps, socket caps, and some finials. Allows electrical wire to pass through pipe.
1/4 IP-18 - 1/2" outside diameter, used on floor lamps, clusters, ceiling fixtures, and floor lamp bases.
3/8 IP - 5/8" outside diameter, used on chandeliers and hanging lamps.
F: designates a female thread - part is tapped having interior threads.
M: designates a male thread - threaded with exterior threads.
Watts: Volts multiplied by Amps
Amps: Watts divided by Volts
Volts: Watts divided by Amps