GENUINE JACK E4 E4S 798D INDUSTRIAL OVERLOCKER UPPER & LOWER KNIFE SET

The Genuine Jack Upper and Lower Overlocker Knife Set is a replacement cutting blade set designed for compatible Jack industrial overlocking sewing machines, including suitable models within the Jack E4, E4S and JK-798D series.

Industrial overlocker knives are essential components of the machine's fabric trimming mechanism, working together to cut excess material from the fabric edge before the overlock stitch is formed.

The upper moving knife and lower fixed knife work together to produce a clean, consistent fabric edge, helping achieve professional overlocking results during garment manufacturing, tailoring and textile production.

Over time, industrial overlocker blades can become blunt, chipped or damaged through regular use, particularly when cutting thicker fabrics or working in high-volume production environments.

Worn overlocker knives can cause uneven fabric trimming, frayed edges, material bunching and inconsistent cutting performance, affecting the quality of the finished seam.

Replacing worn blades with the correct Jack upper and lower overlocker knife set helps restore effective fabric trimming and maintain reliable machine performance.

These replacement knives are suitable for professional industrial sewing environments, including garment factories, tailoring workshops, alteration businesses, textile manufacturers, fashion studios and industrial sewing machine repair workshops.

Please Note: Jack manufactures several different upper and lower knife designs. Compatibility must be confirmed using the original knife part numbers and the exact sewing machine subclass before ordering.

KEY FEATURES

• Genuine Jack upper and lower overlocker knife set
• Includes 1 upper knife and 1 lower knife
• Designed for compatible Jack industrial overlock sewing machines
• Suitable for applicable Jack E4 and E4S models
• Suitable for applicable Jack JK-798D models
• Replacement for worn, blunt or damaged overlocker blades
• Helps restore clean and consistent fabric trimming
• Upper moving knife and lower fixed knife combination
• Designed for industrial overlocking applications
• Suitable for professional garment and textile production
• Ideal for industrial sewing machine servicing and repairs

WHAT'S INCLUDED?

1 × Upper Overlocker Knife / Moving Blade

The upper knife moves against the lower blade during sewing, cutting excess fabric from the edge of the material.

1 × Lower Overlocker Knife / Fixed Blade

The lower knife provides the stationary cutting edge against which the upper knife operates.

Together, these components form the overlocker's fabric trimming mechanism.

COMPATIBLE JACK INDUSTRIAL OVERLOCKERS

The supplied product information references knife variants used across several Jack industrial overlocker ranges.

The following models are relevant to compatibility checks:

Important: This table identifies machine ranges referenced in the supplied information. It does not confirm that one knife set fits every listed model.

Some Jack machines use standard straight knives, while others require angled lower knives or different blade configurations.

The correct replacement must match the original cutting system.

JACK OVERLOCKER KNIFE PART NUMBERS

Several upper and lower knife part numbers are associated with Jack industrial overlocker models.

UPPER KNIFE REFERENCES

• 20619002
• 20119001
• 20719007
• 30119009 / JK-30119009

LOWER KNIFE REFERENCES

• 21317002
• JK20119002
• 20719004

ADDITIONAL KNIFE SET REFERENCE

• 20719050 – Angled upper and lower knife set reference

These references may represent different knife designs, machine subclasses or cutting arrangements.

They are not confirmed interchangeable part numbers.

For this product, I recommend identifying the exact upper and lower blade numbers included in your genuine Jack set before adding them as product specifications or SEO keywords.

WHEN SHOULD OVERLOCKER KNIVES BE REPLACED?

Industrial overlocker knives are subject to continuous wear during fabric trimming.

Common signs that replacement knives may be required include:

• Frayed or uneven fabric edges
• Fabric folding instead of cutting cleanly
• Increased resistance during trimming
• Visible chips or damage to the cutting edges
• Poor trimming performance
• Excessive fabric pulling during overlocking

Replacing worn knives can help restore consistent fabric cutting and improve the appearance of finished overlocked seams.

WHY REPLACE BOTH UPPER AND LOWER KNIVES?

The upper and lower knives work together as a cutting pair.

If either blade becomes worn or damaged, the machine may struggle to trim fabric effectively.

Replacing both knives together can be beneficial when both cutting edges show signs of wear, helping restore consistent cutting performance.

However, correct installation and knife alignment are equally important for effective operation.

PRODUCT SPECIFICATIONS

IMPORTANT COMPATIBILITY INFORMATION

PLEASE CHECK YOUR EXISTING KNIVES BEFORE ORDERING.

Jack industrial overlockers can use different knife designs depending on the model, subclass and cutting mechanism.

Before purchasing, please confirm:

• Your machine's exact model and subclass.
• The part number of your existing upper knife.
• The part number of your existing lower knife.
• Whether your machine uses a standard or angled knife configuration.
• That the replacement knife dimensions and mounting arrangement match your original blades.

If you are unsure which knives your machine requires, please contact Infinity Sewing with your machine model and photographs of the existing blades.

INSTALLATION INFORMATION

For safe and effective operation, replacement overlocker knives must be correctly positioned and adjusted.

Incorrect knife alignment can result in poor cutting performance, excessive blade wear or damage to the cutting mechanism.

We recommend installation by an experienced industrial sewing machine engineer.