MotorbyMotor Universal Window Crank Shaft Extension for GM 16-Spline Shafts — 5/8"–11/16" Length Increase, C-Clip Compatible

If your original window crank or door latch handle sits too close to the door panel after restoration or a new regulator was installed, this compact spline extension gives you the extra length needed without replacing the entire shaft. Designed around the common GM-style splined shafts, it provides a straightforward, reversible solution for older American cars and a surprisingly wide range of domestic and import vehicles.

Will this extension work with my car’s splined shaft?

The extension is made for splined shafts commonly found on many 1950–1990 General Motors models and several other makes. It mates to shafts around 1/2" diameter and uses the standard 16-spline pattern where a C-clip secures the handle. If your shaft measures roughly .41 to .46 inches in diameter and uses a C-clip attachment, compatibility is very likely.

• Fits 16-spline shafts with C-clip handle attachment
• Designed for ~1/2" splined shaft diameters (.41–.46" GM spec)
• Common on Chevrolet, GMC, Pontiac, Buick, Olds, Cadillac
• Often compatible with various domestic and many import models

How much extra length does the extension add and can I trim it?

This specific extension increases the shaft length by roughly 5/8" to 11/16"—enough to clear thicker door panels, insulation, or aftermarket door cards. It is manufactured to that fixed length to ensure a secure spline engagement and reliable fit; shorter versions are not offered, and trimming is not recommended because it may compromise spline engagement or retention.

• Adds approximately 5/8"–11/16" of usable shaft length
• Fixed length for secure spline engagement
• Not supplied in shorter sizes; cutting can weaken fit
• Installs without replacing the regulator or handle

What vehicles does this extension fit and where is it typically used?

The part was developed with broad compatibility in mind: most GM cars and trucks from the 1950s through the 1990s, plus many domestic makes and some import vehicles that adopted similar splined shaft designs. Typical applications include window cranks, door latch release shafts, wing vent cranks and door locks where a 16-spline, C-clip style handle attaches.

• Designed for Chevy, Camaro, Corvette, Buick, Pontiac, Olds, Cadillac and GM trucks
• Compatible with many Jeep, Dodge, Chrysler, Toyota, Honda and other models using similar splines
• Used on window regulators, door latch shafts, vent cranks and locks
• Ideal for restorations and repairs where handle clearance is insufficient

Who is this for: This extension is aimed at classic-car enthusiasts, restorers, mechanics and DIYers who need a simple, reversible way to gain a small but crucial amount of shaft length so handles clear panels or aftermarket materials. It’s especially useful when reassembling older GM vehicles or adapting a regulator and handle setup that leaves the crank too recessed. The product is a low-cost, low-effort alternative to replacing shafts or regulators, and it keeps the original handle attachment method intact for an authentic look and feel.