PTO Extender Adaptor, Female 21 Spline & 1-3/8", Male 6 Spline & 1-3/8", Push-Pin PTO Extender for Tractor Compatible with 70 Horsepower Engine Tractor or Lawn Mower Review

Overview

This isn’t a lawn mower itself—it’s a PTO (Power Take-Off) extender adaptor designed to bridge the gap between your tractor or mower’s driveline and your attachment. Specifically, it converts a female 21-spline, 1-3/8-inch output to a male 6-spline, 1-3/8-inch input, with a push-pin locking mechanism. It’s built for tractors and mowers up to 70 horsepower, making it a niche tool for owners of older or less common equipment who need to mate mismatched spline counts or extend their PTO shaft by a few inches.

Who Should Buy This

• Owners of vintage tractors or mowers with 21-spline outputs who need to run modern 6-spline attachments like brush hogs, tillers, or finish mowers. If your tractor is pre-1980s, this adaptor is a lifeline.

• DIY farmers and homesteaders with compact tractors (under 70 HP) who encounter a spline mismatch when swapping implements. It’s a cheap fix versus buying a whole new PTO shaft.

• Homeowners with mid-size lawn tractors (e.g., older John Deere or Kubota models) that use 21-spline outputs but want to connect a 6-spline snowblower or leaf vacuum. If you’ve got a mismatch in your shed, this saves you a trip to the dealer.

• Budget-conscious equipment users who don’t want to replace a perfectly good attachment just because the spline count doesn’t match. At $42.99, it’s cheaper than a new driveline.

Key Features Breakdown

• Spline Configuration: Female 21 Spline (1-3/8" diameter) to Male 6 Spline (1-3/8" diameter) – This is the core spec. The female end fits a tractor with a 21-spline output shaft (common on older or heavy-duty equipment), while the male end accepts a 6-spline attachment input. The 1-3/8" size is standard for Category 1 and 2 PTO shafts, so it fits most mid-size implements. If your gear uses 1-1/8" or 1-3/4" shafts, this won’t work.

• Push-Pin Locking Mechanism – Instead of a cotter pin or snap ring, this uses a spring-loaded push pin to secure the adaptor to the tractor’s PTO stub. It’s tool-free and quick to engage, but it requires a matching hole in your tractor’s output shaft. Check your tractor—some older models use a different retention method.

• 70 Horsepower Rating – This adaptor is rated for tractors up to 70 HP. That covers most compact and utility tractors (e.g., Kubota L-series, John Deere 3-series, Ford 8N). Exceeding 70 HP risks shearing the splines or damaging the push pin. For heavy tillage or large mowers, step up to a heavier-duty adaptor.

• Material: Likely Carbon Steel or Cast Iron – The listing doesn’t specify the exact alloy, but at this price point, it’s almost certainly hardened carbon steel. It’s tough enough for intermittent use but not indestructible. Expect some surface rust if left exposed.

• Length: Typically 4-6 Inches of Extension – The adaptor adds a few inches to your PTO shaft length. This can help if your implement’s shaft is slightly too short, but it also increases leverage stress. For long-term use, a dedicated custom-length PTO shaft is better.

Pros

1. Solves Spline Mismatches Cheaply – No need to buy a new attachment or modify your tractor’s output shaft. This adaptor lets you run a 6-spline implement on a 21-spline tractor for under $50.

2. Tool-Free Installation – The push-pin design means you can swap it in seconds without wrenches. Just align the holes and push. It’s ideal for quick changes between attachments.

3. Compact and Lightweight – At roughly 1-2 pounds, it won’t add noticeable bulk or vibration to your PTO system. Easy to store in a toolbox or tractor cab.

4. Works with Common 1-3/8" Shafts – This size fits the vast majority of compact tractor implements, from rotary cutters to post-hole diggers. You’re not locked into a niche standard.

5. Budget-Friendly Fix – Compared to a new PTO shaft ($100+) or a spline adapter kit ($80+), this is a low-cost stopgap. Great for occasional use or as a spare.

6. Compatible with 70 HP and Under – Covers the sweet spot for most homeowners and small farms. It’s not overbuilt for a garden tractor, but it’s not underbuilt for a 60-HP utility tractor either.

Cons

1. Not for Continuous High-Torque Use – The push-pin is the weak link. Under heavy load (e.g., tilling hard soil or mowing thick brush), the pin can shear or the adaptor can wobble. It’s fine for light mowing or occasional use, but don’t rely on it for daily commercial work.

2. Adds Stress to PTO Shaft – The extra length increases leverage on the tractor’s output bearing and the implement’s input bearing. Over time, this can cause premature wear. For permanent setups, get a shaft cut to the exact length.

3. Potential Fitment Issues – The push-pin hole on your tractor must align perfectly with the adaptor’s pin. If your tractor’s output shaft has a different retention system (e.g., a snap ring groove), this adaptor won’t lock securely. Measure before buying.

4. No Rust Protection – At this price, don’t expect powder coating or stainless steel. The bare steel will rust if left in the rain. You’ll need to oil it or store it indoors.

Bottom Line

The PTO Extender Adaptor is a practical, low-cost solution for a very specific problem: mating a 21-spline tractor output to a 6-spline implement. It’s best for occasional use on tractors under 70 HP—think hooking up a finish mower on a weekend or running a tiller for a garden plot. If you’re a weekend warrior with mismatched equipment, this $43 fix beats buying new gear. But if you run a high-horsepower tractor daily in tough conditions, skip it and invest in a proper custom PTO shaft. For the right buyer, it’s a solid stopgap—just keep a spare push pin in your toolbox.

Frequently Asked Questions

Q: Will this work on my 1952 Ford 8N tractor?
A: Yes, if your 8N has the standard 1-3/8" 21-spline output (most do). The push-pin must align with the hole on your PTO stub. Measure the hole