$7.99 Each
In stock

Forstner Bit Extender

Item #
86% 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
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.
4.3 / 5.0
48 Reviews
5 Stars
4 Stars
3 Stars
2 Stars
1 Star
Forstner extinction
Works like a charm lol works great just what I expected from Rockler nothing but the best
June 11, 2019
3 months ago
Woodworking Experience:
The shaft!
Got this awhile ago to run some romax and one run was so close I couldn't use the bit I had. Used this to go through the next joist and had just enough to make it through. Perfect length!
May 20, 2019
over 4 years ago
Woodworking Experience:
Works as advertised
Read the description !!
February 20, 2019
7 months ago
Woodworking Experience:
Works great.Very well made.
February 5, 2019
1 year ago
Woodworking Experience:
Forstner bit extender
It works, it was cheap. What else is there to say?
January 25, 2019
8 months ago
Woodworking Experience:
It' s excellent. I have began . working with it
January 5, 2019
9 months ago
Always Aligned
Extender stays aligned even when you have to adjust drill table to continue drilling.
July 27, 2018
1 year ago
Woodworking Experience:
Great product works great .
June 8, 2018
1 year ago
Woodworking Experience:
Perfect for my job
April 3, 2018
1 year 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
1 year ago
Woodworking Experience:
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Browse 9 questions Browse 9 questions and 68 answers
Why did you choose this?
Rockler Store
Need to drill 4 consecutive absolutely straight 7" holes to mount a heavy slab mantel.
Doug H on Aug 29, 2019
Larry B on Jul 27, 2019
Need to drill 4 consecutive absolutely straight 7" holes to mount a heavy slab mantel.
Doug H on Aug 29, 2019
Didn’t have one
Robert B on Aug 10, 2019
Larry B on Jul 27, 2019
There are times this product is useful and necessary.
George C on Jul 18, 2019
Sometimes I need to drill further into the 4x4 treated wood post than the normal bit can reach. Hoping this will help with this issue.
MIKE H on Jul 8, 2019
Only place I could find this item
Thomas W on Jul 6, 2019
I need it.
E T on May 10, 2019
Need an extension for deep holes
Daniel B on Apr 25, 2019
For deeper holes.
J I on Apr 22, 2019
Why not?
Madison D on Apr 6, 2019
hard to find short extension elsewhere
John B on Feb 18, 2019
It should fit my drill bits, and that is what I need.
Susan S on Feb 10, 2019
Extend reach of bit.
Donald V on Feb 4, 2019
needed it
Scott M on Jan 23, 2019
My bits are too short and your extender is a lot less expensive than Woodcrafters (theirs is twice as long and without shipping, costs twice as much as yours with shipping).
David Hykes on Jan 3, 2019
Do not have one.
Richard R on Dec 28, 2018
To use with my lathe
Albert M on Dec 17, 2018
Needed for other projects
Gary L on Dec 13, 2018
Christmas Gift.
Mark S on Dec 2, 2018
Need for single humidor kit
David N on Nov 30, 2018
In case it is needed for deeper holes.
Al on Nov 29, 2018
Nice to have on hand. Filled in the order to qualify for free shipping.
Anthony on Nov 18, 2018
for longer blanks
Steven J on Nov 4, 2018
because they are so hare to find anywhere
JAMES Z on Oct 24, 2018
To make sure there is enough length on my bits.
Darrel G on Sep 28, 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
Didn’t have one
Robert B on Aug 10, 2019
There are times this product is useful and necessary.
George C on Jul 18, 2019
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
What is the OD of the female end? Can I use a 7/8" bit in this extender?
C N on Oct 16, 2018
BEST ANSWER: No......3/8" shanks only
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
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