BRASS AND COPPER
Due to its high rate of wear, brass and copper are no longer viable materials for electrode use (with the exception of small diameter tubing for hole drilling). Brass and copper rods and tubes are available in .008" dia. - 3-1/8" dia. in increments of .001 inch.

TELLURIUM COPPER (TELCO)
The most commonly used metallic electrode material. The element tellurium has been added (0.5 to 1%) for ease of machining. This is tellurium copper alloy 145 (99.5% copper, 0.5% tellurium, 0.01% phosphorus) and comes in squares, rounds and rectangles.
squares are available in 3/8" - 2"
rounds are available in 1/8" - 4"
plates are available in1/4" - 3"
available in lengths up to 72"

COPPER TUNGSTEN
Used when the "safety" of copper is desired, but it provides much better wear resistance. Also used in the EDM'ing of carbide and refractory metals (cobalt, molybdenum, etc.) Composition of 70% tungsten/30% copper is available in
rounds 1/8" - 3-1/2"
squares 1/8" - 2"
plates 3/32" - 2"
tubes.020" - 1"
rods from .009" - .125"

Composition of 60% tungsten/40% copper is available in rolled sheet from .001 - .093".

Composition of 75/25 and 80/20 are available on request.

TUNGSTEN CARBIDE
Available in tube and rod only in O. D. sizes of .005" - .250".

SILVER TUNGSTEN
Used where the higher conductivity of silver is desired. This material is very expensive, about five times the cost of copper tungsten. Rounds, squares and rectangles are 75% tungsten/25% silver.

TUNGSTEN
Tungsten is used when wear is a consideration, not speed. When combined with copper, machining rates will increase. Tungsten carbide (90% tungsten and 10% cobalt) material is very strong and durable which results in good wear resistance, but it does not cut very fast. Available in wire only, both spools and straight lengths, from .0007" - .060" dia.

Source: The EDM Handbook by E.B. Guitrau