$7.99 Each
Oversold Until 12/05/2018

Forstner Bit Extender

Item #
88% of 100

Get an extra 2-1/2" of reach into deep holes with this Forstner bit extender. Great for rustic furniture and joining wide timbers. Also works with any other style of 3/8" shank drill bit greater than 1" in diameter. Forstner bit sold separately.

  • Works with 1" diameter bits or larger, smaller bits will not allow extender to enter the hole
  • 3/8" shank with triangular flats for positive grip
  • 2 hex-head screws securely grip drill bit
  • Socket for drill bit accepts 3/8" shank bit, and extends 1-1/2" into extender
  • Total shank measures: 2-3/16" long - flattened triangular section: 1-1/2" long
(1) Forstner Bit Extender
More Information
Brand Insty-Bit
Manufacturer Part Number 4" EXTENDER
Weight 0.2600
Tech Spec
  • Length: 4"
  • Width: 3/4" at Widest Section
Tech Docs No
Bit Material No
Bit Size No
Prop 65 WarningWARNING: Cancer & Reproductive Harm - www.P65Warnings.ca.gov

Prop 65 WarningWARNING: Drilling, sawing, sanding or machining wood products can expose you to wood dust, a substance known to the State of California to cause cancer. Avoid inhaling wood dust or use a dust mask or other safeguards for personal protection. For more information go to www.P65Warnings.ca.gov/wood.
4.4 / 5.0
40 Reviews
5 Stars
4 Stars
3 Stars
2 Stars
1 Star
Always Aligned
Extender stays aligned even when you have to adjust drill table to continue drilling.
July 27, 2018
2 months ago
Woodworking Experience:
Great product works great .
June 8, 2018
4 months ago
Perfect for my job
April 3, 2018
5 months ago
Woodworking Experience:
That little extra
Bought for a project where I had to drill into a old baseball bat in order to make a mug. Was not sure it was going to work with the forester bit I was using, but worked as needed.
Thanks Rockler team
March 5, 2018
7 months ago
Woodworking Experience:
It's a great extension. Very strong!
February 27, 2018
over 4 years ago
Woodworking Experience:
Love it, just the right size!
January 16, 2018
8 months ago
Woodworking Experience:
Does its job. Good product
January 8, 2018
9 months ago
Did what I intended without any problems.
September 14, 2017
1 year ago
Woodworking Experience:
A must have
This is a necessary accompaniment to any Forstner bit kit. A low price so just get it. Even if you use it sparingly, it is worth it to have it when you need it. Just get it.
July 27, 2017
1 year ago
Woodworking Experience:
Forster extension
Just as advertised.
July 7, 2017
1 year ago
Start typing your question and we'll check if it was already asked and answered. Learn More
Browse 8 questions Browse 8 questions and 67 answers
Why did you choose this?
Rockler Store
because I cant buy long forstner bits
John H on Aug 19, 2018
I needed to drill deeper holes
Marion H on Jun 17, 2018
because I cant buy long forstner bits
John H on Aug 19, 2018
It was on sale and had more than 4.0 stars.
Dan H on Aug 1, 2018
I needed to drill deeper holes
Marion H on Jun 17, 2018
Bill B on May 9, 2018
drill deeper holes
JOSH J on Apr 20, 2018
can use it on some of my turning projects
richard m on Apr 4, 2018
for purchased tool
Brian R on Mar 17, 2018
Longer range
Randy C on Mar 8, 2018
To go with kit purchase
Rick H on Mar 1, 2018
Not sure the bit is quite long enough . Say's it doesn't work with bits smaller than an inch. Say's it's 3/4" at widest point. My bit is 7/8" Going to take my chances .
Bryan M on Mar 1, 2018
price and reviews
Jose M D on Feb 16, 2018
Need an extender for my bits
Robby on Feb 15, 2018
Good price
John W on Feb 12, 2018
I have a mortiser but the throat is too deep and my bits are too short to fit into the chuck.
Ivan G on Feb 7, 2018
I purchased the Forstner Bit Set and think I may need this for my projects.
Gerald B on Jan 31, 2018
Need this with forstner bit
John H on Jan 25, 2018
Need to drill deeper holes
DOUG A on Jan 5, 2018
on my husband's wish list
Vicky L T on Dec 17, 2017
Bought it just in case I need it sometime.
Eric R on Dec 13, 2017
I needed it and the price was right
Gene M on Dec 1, 2017
complement the bit set
Paul B on Nov 25, 2017
need it for wood turning, boring out pepper mills.
Reuben R on Nov 11, 2017
Will use to extend forester drill bits for vases and other projects on the lathe requiring deep drilling.
B I on Oct 25, 2017
Needed it
D R on Oct 17, 2017
only 1 offered
dom n on Oct 15, 2017
for a project
jay r on Oct 13, 2017
Hollowing out a 6 inch tree branch so I need the extra length
Eric S on Oct 6, 2017
need more reach with bits
walter b on Aug 25, 2017
needed to increase depth for wood turning projects
Robert T on Jun 5, 2017
building desk and need to through thick surface
Deb L on Jun 5, 2017
Can't find it locally.
Anthony N on May 28, 2017
Need to drill over 5 1/2 inches.
Gordon P on May 11, 2017
needed for special projects
Ron S on Apr 14, 2017
I am making replacement wood face for my workbench end vice and need the extra length.
Ron R on Apr 5, 2017
For my woodworking projects
Vickie R on Mar 11, 2017
needed to drill a deep hole for project. when it arrived I found it to be very heavy duty and I am very happy with it
Russ H on Mar 2, 2017
Setting up shop
EMMITT J on Mar 1, 2017
Scott M on Feb 17, 2017
I have a bench to drill press and this extender adds to the drill length.
Kennedy F. R on Jan 25, 2017
handy for deep mortise pockets.
LARRY L on Jan 5, 2017
Good compliment to the bit set
Ronald F on Dec 26, 2016
for a project
Michael W on Nov 8, 2016
need to bore deep hole
Albert S on Nov 8, 2016
needed one a few days ago
D A on Oct 26, 2016
Allows to bore deeper into clean edges holes. The extension allows the forstner bits to be drilled deeper using the drill press.
Darrel S on Oct 23, 2016
JOSEPH C on Oct 13, 2016
to drill deeper
Lisa T on Sep 25, 2016
needed for making pepper mills
Delmar V on Sep 23, 2016
Give me that extra depth that is required on some projects.
Kenneth G on Sep 12, 2016
Needed a longer hole
Wilbur B on Sep 1, 2016
It was on sale and had more than 4.0 stars.
Dan H on Aug 1, 2018
Bill B on May 9, 2018
will this work with the Jig IT........?
Billy S on Dec 14, 2015
BEST ANSWER: Sorry, I don't know. I bought it to use with a forstner bit and Chuck in lathe tail stock.
can you connect two 2.5 " extenders to my bit to drill a deeper hole?
M G on Dec 14, 2015
BEST ANSWER: No you can not. The ID of the extender is .375 inches and the Shank OD is .403 (Too Big)
I was hoping to do this too but the shank is almost a 1/32 too big.
What is the ID of the set screw end?
Jay R on May 11, 2015
BEST ANSWER: I measure at 3/8". Forstner bit is a snug fit. I use Bosch and Porter Cable bits.
what is the diameter of the extender? in other words what is the smallest forstner bit i can use?
Troy M on Mar 7, 2017
BEST ANSWER: It's designed for 3/8", I would think anything smaller would be offset and not be true. The set screws are both on the same side
Can Forstner bit extender be used with Rockler drill guide? Or are long-shank bits required?
Neal G on Apr 2, 2018
Forstner Bit Extender
Forstner Bit Extender
Rockler JIG IT® Drill Guide
Rockler JIG IT® Drill Guide
BEST ANSWER: A long shank bit, such as Rockler item 10117, is required with this jig.
will this work with the portable drill guide with Ryobi 3 flat sided Forstner bits?
Elenita E on Aug 27, 2016
BEST ANSWER: I have round round w/flat and 6 sided bits that all work well. I use it in a chuck in the tail stock of a lathe. Quite a bit of pressure and it has held secure each time
I used the extender for three times, both set screws are now stripped. I need to replace them. What are the measurements of these set screws? Thank you.
Louise D on Jul 6, 2017