FIP3500-0.75 Pulley Idler Flat Compatible with Rotary Mower 3/4" X 3-1/2", Replace 13-10150

What It Is

The FIP3500-0.75 is a flat idler pulley designed to guide and tension the belt on rotary mower decks. It’s a direct replacement for OEM part 13-10150, commonly used on mid-size zero-turn and riding mowers.

Fitment & Compatibility

Before buying, verify these three measurements:

• Shaft diameter: Must be exactly 3/4" (the bore size of this pulley). Measure your existing pulley bore or the spindle shaft it mounts on.
• Pulley outer diameter: This pulley is 3-1/2". Check your old pulley’s OD—if it’s different, belt tension and routing may change.
• Pulley width: Flat profile, not grooved. Ensure your belt is a flat (not V or cogged) type.

This pulley is a direct fit for many Rotary mower models and aftermarket decks using the 13-10150 number. It does NOT fit all mowers—check your deck’s parts diagram or measure the existing pulley’s bore and OD. No brand-specific adapter needed; universal fit for 3/4" shafts.

Key Things to Know

• Quality: Steel construction with a sealed bearing. Should hold up well under normal residential/light commercial use. One review suggests it’s a solid budget alternative to OEM.
• Installation difficulty: Easy—remove the old pulley bolt (usually a hex or Torx), swap the pulley, and retighten to manufacturer torque spec (typically 20-30 ft-lbs). No special tools required.
• Common gotcha: Flat idler pulleys can be confused with V-groove or tensioner pulleys. If your original has a groove, this won’t work. Also, check that the belt width matches the pulley face—some decks use 1/2" or 5/8" belts.
• Spacer or shim needed?: Some decks require a spacer between the pulley and deck. If your original had one, reuse it. If not, this pulley should mount flush.

Should You Buy It

If you need a direct replacement for a 13-10150 flat idler pulley on a 3/4" shaft, this is a cost-effective, well-rated option. It’s ideal for DIY repairs where OEM parts are overpriced or backordered. Skip it if your pulley bore is different (e.g., 1/2" or 1") or if your deck uses a grooved or spring-loaded tensioner pulley.