Description
M49C Machine-Gun Ring-Mount Carriage Lock Washer for M5-Series High-Speed Tractors, A188017 / 5188017
Item Overview
This original keyed lock washer was used in the M49C machine-gun ring-mount carriage installed on M5-series high-speed tractors. Its exact military nomenclature is “Washer, lock: inner, roller clamp screw.”
The washer secures the roller-clamp hardware on the movable gun carriage, commonly called the carriage or skate. This assembly traveled around the circular ring and allowed the gunner to move a mounted Browning M2 .50-caliber machine gun through a full 360-degree field of fire.
This is a ring-mount carriage part. It is not a transmission, suspension, final-drive, or other drivetrain washer.
Identification and Features
- Exact nomenclature: Washer, lock: inner, roller clamp screw
- International Harvester part number: A188017
- U.S. Ordnance part number: 5188017
- NSN: 5310-00-518-8017
- Federal item name: Washer, Keyway
- Primary application: M49C machine-gun ring-mount carriage
- M5-series catalog: SNL G-162
- Cross-catalog reference: G-176
- Material: Steel
- Finish: Phosphate
- Center-hole diameter: 0.703" minimum to 0.719" maximum
- Outside diameter: 1.125" nominal
- Thickness: 0.057" minimum to 0.062" maximum
- Number of external keys: Two
- External key length: 0.125" nominal
- External key width: 0.125" minimum to 0.156" maximum
The washer was made with two external locking keys. The outer edge was prebent 0.125 inch at a 90-degree angle across each keyway. These features helped prevent the roller-clamp screw from turning after installation and adjustment.
Application and Function
The M49C ring mount used a circular track above the vehicle’s crew area. A movable carriage traveled around the track and supported the machine-gun cradle, ammunition equipment, and related hardware.
Rollers guided the carriage as it moved around the ring. Clamp screws secured and adjusted the roller hardware. Washer A188017 locked the inner roller-clamp screw in position, helping maintain the carriage’s adjustment during vehicle movement and weapon operation.
This small part was important to the safe and dependable movement of the gun carriage. It should not be confused with a general-purpose hardware washer.
Catalog Markings
The package marking “FOR M5 TRACTOR” and its SNL G-162 reference identify this example as M5-series tractor stock.
The G-176 marking refers to the M20 Armored Utility Car catalog. The M20 used related M49-series ring-mount hardware, which explains why the same component could appear under more than one military parts catalog.
Historical Background
International Harvester developed and manufactured the 13-ton High-Speed Tractor M5 as an artillery prime mover during World War II. The tracked vehicle carried a gun crew, ammunition, and equipment while towing weapons such as the 105mm howitzer, 155mm howitzer, and 4.5-inch gun.
The first M5 tractors were accepted in May 1943. A total of 5,290 were produced. The later M5A1 entered production in May 1945 and added a steel cab, revised seating, and other changes.
The M49C ring mount was factory-installed on the M5A1. A field modification allowed the mount to be added to some later M5 tractors, but it was not standard on every early M5.
When equipped with the ring mount, the tractor could carry a flexible Browning M2HB .50-caliber machine gun for defense against aircraft and ground threats. The mount provided full manual traverse around the vehicle’s upper structure.
M49-series ring mounts were also used on armored cars, half-tracks, trucks, amphibious vehicles, artillery tractors, and recovery vehicles. This wide use explains the shared catalog references found on surviving replacement parts.
Condition
This is an original military-surplus lock washer identified by its labeled packaging. The washer may show finish wear, scratches, discoloration, light oxidation, or other signs of long-term storage.
Original packaging may show fading, stains, tears, handwriting, or storage wear. Please review the product pictures for the represented condition and markings.
Ideal For
- M5 and M5A1 high-speed tractor restorations
- M49 and M49C ring-mount projects
- Browning M2HB vehicle-mount displays
- M20 Armored Utility Car research
- World War II military-vehicle collections
- International Harvester military-equipment displays
- Museums and historical exhibits
This listing is for the keyed lock washer shown or represented in the product pictures. The M49C ring mount, carriage, roller hardware, Browning machine gun, vehicle, and other components are not included unless pictured or specifically stated.
Approx length 1.125", Approx width 1.125", Approx height .057"-.062", Approx weight 0.1 lbs.
Pictures are stock images of our inventory. Unless otherwise noted, you will not be receiving the exact item shown in the pictures. The pictures are representative of the item's general condition. The item you receive might be slightly better, or worse, condition than was shown in the pictures.
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