Choosing Your Drill Guide: Egg Cup Bushing Holders, Mini and Dog Bone Guides for SF and Threaded Bushings
By the Wescon Engineering Team · Last updated October 8, 2026A drill guide holds the drill bit square to the aircraft skin so every hole comes out round and where you marked it, with a slip fit or threaded bushing doing the guiding. Drilling a hole at the wrong angle causes problems. Two issues come up often, and both are easy to run into even with careful work:
- An off-axis hole is not perpendicular, so it comes out elongated instead of round. This weakens the fastener's grip and can force the part to be scrapped, an expensive mistake in aerostructure work.
- Even with steady hands, curved or slippery surfaces are hard to control. The drill bit can wander before it bites into the material, starting the hole in the wrong spot.
Photo: Wescon Industries Inc., CC BY 4.0
Photo: Wescon Industries Inc., CC BY 4.0A drill guide solves both problems. It holds the bit at a true 90-degree angle to the surface and keeps it from wandering, so every hole comes out straight, round, and in the right place. It serves a simple, yet critical function in the workshop.
How to Choose Your Drill Guide
Step 1: Choose your bushing type
Decide which bushing type you will use, or check what your workplace already standardizes on. The two main options are Slip/Fixed (SF) renewable bushings, sold in the aircraft trade as slip fit bushings, and threaded bushings. Both types are industry standards.
Step 2: Choose your housing type
Your housing choice depends on where you are working. For easy-to-access parts, the egg cup bushing holder, also called an egg cup drill guide, drill stand or drill cup, is a good fit. Its shape improves ergonomics and gives a stable base. For tight spaces, the mini drill bushing holder is the better choice.
Photo: Wescon Industries Inc., CC BY 4.0
Photo: Wescon Industries Inc., CC BY 4.0
Photo: Wescon Industries Inc., CC BY 4.0
Photo: Wescon Industries Inc., CC BY 4.0SF bushing drill guides
Threaded bushing drill guides
These bushing holders are made from anodized aluminum for durability and wear resistance.
Wescon manufactures both SF bushing and threaded bushing housings, so either option is covered.
Step 3: Choose your footpiece material
Your work surface determines which footpiece to use. Both egg cup and mini drill guides come with two standard options:
Heavy duty plastic  | Anodized aluminum  | |
|---|---|---|
| Characteristics | surface hardness lower than most aerospace alloys, non-abrasive | high surface hardness, strong structural rigidity, excellent thermal conductivity |
| Advantage | gives a no-mar contact patch that prevents circular scoring or "halos" on finished surfaces | gives maximum wear resistance, and holds up in high-friction, high-heat applications without the degradation or deformation seen in plastic |
| Use on | certain aluminum alloys, painted surfaces | titanium alloy work surfaces, carbon fiber |
Number of legs
To choose the number of legs on your drill bushing holder:
- 3-leg footpieces work better on contoured or slightly cambered surfaces.
- 2-leg footpieces are mostly used to avoid an obstruction, such as a protruding fastener head, a channel, or any other linear obstruction running through the marked point.
For extremely curved or contoured aerostructure surfaces, where a standard 3-leg footpiece can't sit stable, choose the WES5703-2-T tripod base drill bushing holder. For a step by step guide, see how to drill straight holes on curved surfaces.
We recommend keeping both an egg cup and a mini drill guide on hand, along with an assortment of bushings, in a single kit. That is why we offer WESKIT005 for threaded bushing users, and WESKIT009 for engineers who prefer SF bushings. To keep several drill sizes set up at once, the WESKIT006 drill bushing kit has three threaded egg cup guides and nine 1/2-13 threaded drill bushings.
Special Use Cases and Accessories
Special application 1: Improving mini drill guide handling
The WES5620 mini drill guide series is built for tight-space applications, which means its compact form factor can make it hard to hold comfortably in some jobs.
For a better hold, we offer the WES5630 series handle that attaches to compatible drill guides for better grip and control: WES5631 for the 3/8"-16 guide and WES5632 for the 1/2"-13 guide.
Photo: Wescon Industries Inc., CC BY 4.0Special application 2: Drill hole resizing
Some precision drilling jobs need a two-stage process. First, you drill a precision hole using a bushing with a smaller inner diameter. Then you ream the hole to its final size. This requires two SF bushings for the job.
The dog bone guide holds two SF bushings in a single drill block, so one guide covers both the drilling and the reaming.
Photo: Wescon Industries Inc., CC BY 4.0Drill Guide Selection Tables by Bushing Size
Check which bushing type you use, then go to the matching table below. Go to Table 1 if you use an SF bushing. Go to Table 2 if you use a threaded bushing.
Table 1: SF bushing guides
View the ANSI code of your SF bushing (in the format SF-XX-XX) and find the matching guide type below.
| SF bushing dimensions | Mini drill guides | Egg cup drill guides | Dog bone drill guides |
|---|---|---|---|
| SF-20-12 (5/16" x 3/4") | — | WES5723-1 | — |
| SF-32-8 (1/2" x 1/2") | WES5723 | WES5723-2, WES5703-2-T | WES5400-1-500 |
| SF-32-12 (1/2" x 3/4") | WES5723 | WES5723-2, WES5703-2-T | WES5400-1-750 |
| SF-32-16 (1/2" x 1") | WES5723 | WES5723-2.5 | WES5400-1-1000 |
| SF-48-12 (3/4" x 3/4") | — | WES5723-3 | WES5400-2-750 |
| SF-48-16 (3/4" x 1") | — | WES5723-3 | WES5400-2-1000 |
Table 2: Threaded bushing guides
Check the thread size on your drill guide and find the matching style below.
| Threaded bushing dimensions | Mini drill guides | Egg cup drill guides |
|---|---|---|
| 3/8"-16 (WES5501) | WES5621 + accessory: handle WES5631 | WES5721 |
| 1/2"-13 (WES5502) | WES5622 + accessory: handle WES5632 | WES5722 |
Choosing the right drill guide depends on three things: the bushing type, the housing, and the footpiece. With the right match, you get straight, accurate holes every time, no matter the surface or the job. Every Wescon drill guide, bushing and kit in this article is made in USA.
Browse egg cup bushing holders and mini drill guides →Contact our engineering team →
Frequently asked questions
What is an egg cup bushing holder?
An egg cup bushing holder is a drill guide with a cup-shaped anodized aluminum body that holds a slip fit (SF) or threaded drill bushing square to the work surface. The drill bit enters at 90 degrees and can't wander, so the hole comes out round and where you marked it.
Should I use a plastic or aluminum foot on an egg cup bushing holder?
Use the heavy duty plastic foot on painted surfaces and softer aluminum alloys, where it won't leave circular marks. Use the anodized aluminum foot on titanium and carbon fiber, or in high-friction, high-heat work where plastic would wear or deform. The holder body is anodized aluminum either way.
Which bushing sizes fit an egg cup bushing holder?
Wescon egg cup bushing holders take SF bushings SF-20-12, SF-32-8, SF-32-12, SF-32-16, SF-48-12 and SF-48-16, and 3/8"-16 and 1/2"-13 threaded bushings. The selection tables above match each bushing to its holder.
Read next: drill bars, the snatch block for hole repair
A drill guide starts a new hole square. When the hole already exists and is crooked or mismatched, the tool is a drill bar, the one mechanics call a snatch block or steam boat. It clamps to the part with clecos through a slot and holds the same SF or threaded bushing over the old hole so you can ream it round and on center. Wescon makes them for 1/2 and 3/4 in SF bushings and for 3/8-16 and 1/2-13 threaded bushings, single ended, double ended and with swivel heads. Read the drill bar guide.
