New video from MadBull Airsoft... "The Ultimate ball bearing spring guide features a slightly thinner diameter shaft to accommodate springs of all sorts, making it more forgiving for both the spring and piston to compress.  The spring guide's shaft is built-in with the top bearing plate to allow more rigidity and maximum spring decompression.  As a spring decompresses, the bearings allow full twisting, adding improved rounds-per-second and maximum power.

• Thinner guide shaft for easy, stress-fee spring compression
• One piece bearing top plate and guide shaft.
• Loose bearings for maximum spring twisting.
• Smooth anodized finish.
• Machined lightweight CNC aluminum.

More information here."