Eemann Tech Single Stack Magazine Spring for 1911 and clones.
Specifications:
• Caliber: 9x19mm
• 13 coils
• Varied, progressive structure provides constant pressure with greatly increased spring performance and life.
• Magazine spring made of steel according to UNE10270-1-SM norm, with thermic treatment.
• +10% stronger from the factory magazine spring.
• Extra power magazine springs help improve feeding with extra power recoil springs and when factory springs have weakened. 
No fitting required and instant installation in most cases. In some cases, pistols may differ in production or pre-modified and may require assistance of certified gunsmith for installation.