Baby Lock Lower Knife 405910201A

This replacement lower knife, part number 405-9102-01A, fits a range of Baby Lock BL3, BL4, and BL5 series sergers plus the EF405 and EF405M, along with the Simplicity SL600, SL660, and SL700. The lower knife is the stationary blade that the upper knife cuts against as you serge. When its edge becomes dull or chipped, the trim turns ragged and the upper knife wears faster. A fresh lower knife restores a clean, precise cut.

The lower knife lasts longer than the upper knife, but it does wear over time. Replace the lower knife only when its condition or cutting performance warrants it, and inspect the upper knife at the same time. This is an affordable part that helps keep an older serger performing like new. Confirm your model in the specifications below.

Specifications

Installation Tips

• Unplug the serger before accessing the cutting area.
• Consult your exact model's manual before removing the fixed lower knife. Contact a qualified service technician if replacement or alignment is designated as a service procedure.
• Follow the specified lower-blade height and alignment for your model; do not assume the same setting applies to every compatible serger.
• After correct installation and alignment, turn the handwheel slowly by hand to check that the knives pass each other without interference.
• Test on scrap fabric before sewing your project. If cutting remains poor, have the machine checked by a qualified service technician.

Signs It Is Time to Replace

• Fabric edges look chewed, frayed, or uneven instead of cleanly trimmed.
• Threads catch or the fabric drags as it passes the knives.
• The blade has visible nicks, dull spots, or damage after sewing over a pin.
• Inspect both cutting edges and replace a worn or damaged blade as needed. The fixed lower blade generally lasts longer and does not automatically need replacement when the upper blade is changed.

Model compatibility is listed from published cross-reference information. If your exact model is not listed, please contact our team before ordering so we can help confirm fit.

Why Buy From World Weidner?

Buying this lower knife from World Weidner means getting a correctly identified replacement part from a team that stocks and services serger parts every day. We list the part number and compatible models up front, ship quickly from Oklahoma, and back every order with the perks below. If you are unsure about fit, our support team can help you check your model before you order.

• 60-Day Money-Back Guarantee: We offer a generous 60-day full satisfaction and money-back guarantee for risk-free shopping on your purchase.*
• Low Free Shipping Threshold: Enjoy free shipping within the contiguous United States on all qualifying orders over our low minimum threshold.
• Fast Order Delivery: Orders ship quickly from our central Oklahoma warehouse, usually arriving at your doorstep within 1 to 4 business days.
• Loyalty Rewards Program: Earn 5% back on every purchase online and in-store. These points can be saved up and redeemed for discounts on anything we carry.
• Referral Bonus Perks: Take advantage of our "Give $10, Get $10" program that rewards both you and a friend with coupons for future orders and accessories.
• Interest-Free Financing: We partner with popular payment platforms to offer flexible, interest-free installment payments at checkout so you can start creating today.
• In-House Customer Support: Our dedicated, knowledgeable team, including factory-trained service technicians, is available by phone, live chat, or email to assist with part identification, model compatibility questions, installation guidance, and project troubleshooting.
• Massive Interactive Showroom: Check out our 18,000-square-foot physical Creative Center in Oklahoma City for hands-on product demos, direct support, and community classes.