Introduction
This manual provides essential information for the proper use, maintenance, and troubleshooting of your Master Lock Keyed Padlock, Model 6321. Designed for high security, this padlock features a durable construction with a boron alloy shackle and steel body, offering reliable protection for your valuables.
Product Features
- Shackle Material: Hardened Boron Alloy for enhanced cut resistance.
- Body Material: Laminated Steel for strength and durability.
- Body Width: 2-1/8 inches.
- Shackle Diameter: 5/16 inches.
- Key Type: Alike, with 2 keys included.
- Security: High security design with 5 pins.
- Weather Resistance: Yes, suitable for outdoor use.
- Shackle Type: Shrouded for added protection against prying and cutting.

Figure 1: Front view of the Master Lock 6321 Keyed Padlock, showcasing its robust design and shrouded shackle.
What's in the Box
Upon opening the product packaging, you will find the following items:
- 1 Master Lock 6321 Keyed Padlock
- 2 Alike Keys
Setup
- Unpack: Carefully remove the padlock and keys from the packaging.
- Inspect: Examine the padlock for any signs of damage or manufacturing defects. Ensure the shackle moves freely when unlocked and locks securely when closed.
- Key Identification: Identify the two identical keys provided. These keys are "alike," meaning they will open any padlock in a set of similarly keyed locks.
- Test Operation: Before deployment, insert a key into the keyway and turn it to ensure smooth operation of the locking mechanism.

Figure 2: The Master Lock 6321 Padlock shown with its two accompanying keys and key dimensions.
Operating Instructions
To Unlock the Padlock:
- Insert one of the provided keys fully into the keyway at the bottom of the padlock.
- Turn the key clockwise approximately 90 degrees. You will feel a slight click as the locking mechanism disengages.
- Pull the shackle upwards to open the padlock.
- Remove the key by turning it counter-clockwise back to its original position and pulling it out.
To Lock the Padlock:
- Ensure the shackle is fully inserted into the padlock body.
- The padlock will automatically lock upon closing the shackle. No key is required to lock it.
- Gently pull on the shackle to confirm it is securely locked.
Important: Always keep a spare key in a secure location. Avoid forcing the key if it does not turn smoothly.
Maintenance
Regular maintenance ensures the longevity and reliable operation of your Master Lock padlock.
- Lubrication: Periodically apply a small amount of graphite lubricant or a silicone-based spray into the keyway and around the shackle opening. This helps prevent corrosion and ensures smooth operation, especially in harsh environments. Avoid oil-based lubricants as they can attract dirt.
- Cleaning: Wipe the padlock body with a clean, dry cloth to remove dirt and debris. For stubborn grime, a damp cloth can be used, followed by thorough drying.
- Storage: When not in use, store the padlock in a dry environment to prevent moisture buildup.
- Key Care: Handle keys with care. Avoid bending or damaging them, as this can impair the lock's function.
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| Key does not insert or turn smoothly. | Debris in keyway, bent key, or lack of lubrication. | Clean keyway with compressed air. Inspect key for damage. Apply graphite lubricant to keyway. Do not force the key. |
| Shackle is stiff or difficult to open/close. | Corrosion, dirt buildup, or lack of lubrication around the shackle mechanism. | Clean around the shackle entry points. Apply a silicone-based lubricant to the shackle and its entry points. |
| Padlock jams and won't unlock. | Internal mechanism issue, extreme weather conditions, or excessive force applied. | Apply lubricant and gently try to turn the key. If the issue persists, contact Master Lock customer support. Avoid using excessive force, which can damage the lock or key. |
Specifications
| Attribute | Detail |
|---|---|
| Model Number | 6321 |
| Brand | Master Lock |
| Product Dimensions (L x W x H) | 4 x 2.1 x 1 inches |
| Weight | 1 Pound |
| Shackle Diameter | 5/16 inches |
| Shackle Height | 3/4 inches |
| Shackle Width | 7/8 inches |
| Shackle Material | Hardened Boron Alloy |
| Body Material | Laminated Steel, Iron Shroud |
| Number of Pins | 5 |
| Key Type | Alike |
| Number of Keys | 2 |
| Weather Resistant | Yes |
| High Security | Yes |
| Rekeyable | Yes |
Warranty and Support
For information regarding product warranty, returns, or technical support, please contact Master Lock directly through their official channels. You can visit the official Master Lock store for more details and contact information:
Visit the Master Lock Store on Amazon
Please have your product model number (6321) and ASIN (B000E2NMWC) available when contacting support.





