Genuine Unistrut P2950-EG 4 Wheel Trolley Assembly for use with P1000, P1001, P5000, P5001, P5500, P5501 and All 1-5/8" or Taller Strut Channel TROLLEY ASSEMBLY - 4 wheel Unistrut trolley assembly. FOR USE WITH - P1000, P1001, P5000, P5001, P5500, P5501 and All 1-5/8" or Taller Strut Channel. SILVER FINISH - Electro-Galvanized Zinc; ASTM B633, Type III. HOLE DIAMETER - 9/16" (14mm). HOLE SPACING - From End: 13/16" (21mm), On Center: 1-7/8" (48mm).