For a pipe or valve penetration through tile, the Bosch HDG138QA is a diamond hole-saw kit with one 1-3/8-inch cutter, a mandrel and an AutoStart pilot bit; Bosch shows it for hard tile and stone. For small holes for anchors and screws, the Bosch GT2000 is a four-piece carbide-tipped glass and tile bit set in 1/8, 3/16, 1/4 and 5/16 inch. Check the hole size on the fixture or escutcheon drawing first; the HDG138QA cuts one size only.
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A diamond hole saw, a small hollow core bit and a pointed glass-and-tile bit do not all perform the same job. Match the required opening and cutting format first.
Diamond hole saw or glass-and-tile drill bit?
| Example | Format | Included opening sizes | Check first |
|---|---|---|---|
| Bosch HDG138QA | Diamond hole-saw kit | One 1-3/8-inch cutter | Exact material, arbor and cooling requirements |
| Bosch GT2000 | Four carbide-tipped glass/tile bits | 1/8, 3/16, 1/4 and 5/16 inch | Specific tile or glass approval and rotary tool fit |
The diamond hole saw cuts around a core rather than clearing the entire opening with a conventional pointed bit. A four-piece small-hole set does not replace a larger hole saw, and a three-piece hole-saw kit does not necessarily include three cutter sizes.
Bosch HDG138QA: one cutter with starting hardware
Choose HDG138QA when the required opening is 1-3/8 inch and the exact material and tool arrangement are approved for that kit. The current Bosch model table (maker page: www.boschtools.com/us/en/diamond-hole-saw-sets-43652-ocs-ac/) lists one mandrel, one AutoStart pilot bit and one hole saw.
The checked standard new Amazon.com offer showed stock and exact HDG138QA model and part fields. It was the three-piece set, not the larger HDG7 or HDG11 assortment.
Skip it when the fixture drawing requires another hole size or the required compatible arbor and operating instructions cannot be established for the received kit.
Current Bosch family pages reference Power Change Plus while also retaining AutoStart kit contents. Confirm the actual arbor generation and compatible components rather than combining old and new parts by appearance.
Check Bosch HDG138QA diamond hole-saw kit on Amazon →
Bosch GT2000: smaller glass-and-tile holes
Choose GT2000 when its four diameters and the maker’s glass/tile application match the actual job. The current Bosch page (maker page: www.boschtools.com/us/en/glass-tile-drill-bit-sets-43612-ocs-ac/) lists 1/8-, 3/16-, 1/4- and 5/16-inch carbide-tipped bits for rotary drills/drivers.
The checked standard new Amazon.com offer showed stock with exact model and part number GT2000. This is the four-piece set, not GT3000.
Skip it for a larger fixture penetration or any material not confirmed for the exact bit. A general glass-and-tile label should not be extended to every porcelain, stone or glass product.
The pointed bit and the hollow diamond cutter have different starting arrangements. Do not copy the method for one onto the other simply because both are sold for tile-related work.
Check Bosch GT2000 glass and tile bit set on Amazon →
Identify ceramic, porcelain, stone and glass first
Record the surface material before choosing a cutter. Tile appearance alone does not identify its composition or the construction behind it.
For porcelain, verify that the exact cutter and its current instructions expressly cover the material. Do not infer approval from a broad family label or from an accessory that worked on a different tile.
For glass, identify the type and obtain the appropriate manufacturer guidance. This is not a procedure for attempting holes in an unknown glass panel.
For a finished wall, the tile is only one layer. Backer, waterproofing and concealed services can change what work is appropriate and how the penetration must be completed.
If the material or wall construction cannot be established, resolve that uncertainty before choosing a drilling method. A cutting accessory cannot identify a hidden pipe or cable.
Choose the opening from the fixture drawing
Start with the exact fixture’s required opening, location and allowable clearance. Do not choose a cutter solely from the nominal size printed on a pipe or fitting.
The finished trim also matters. Confirm that the planned opening remains within the trim’s intended coverage and that the waterproofing or sealing detail remains possible.
Our escutcheon guide covers the separate trim choice. An oversized plate does not automatically make an incorrectly positioned or excessively large hole acceptable.
For a small mounting hole, use the mounting system’s requirements rather than substituting the size of a convenient bit. A fitting penetration and an anchor hole are different dimensions.
Verify the complete arbor and cutter arrangement
A bare hole saw and a kit containing a mandrel are different purchases. The Bosch individual-cutter table (maker page: www.boschtools.com/us/en/diamond-hole-saws-43883-ocs-ac/) lists HDG138 separately from HDG138QA.
Match the cutter, arbor, pilot arrangement and chuck to the actual tool. A similar diameter or familiar quick-change name does not establish that two generations of parts connect correctly.
Check what the received package includes before assuming a starter or adapter must be ordered separately. Keep the full model codes with the accessories so replacements can be identified later.
Do not interpret an “impact drill/driver” category label as permission to use hammer action on tile. Establish the required operating mode from the exact accessory and power-tool instructions.
Wet and dry use must be product-specific
Follow the exact cutter’s cooling and tool requirements. An older Bosch catalog discusses water use and restricts the machine arrangement; that document does not establish every current package’s complete procedure.
For comparison, the current Milwaukee 49-56-0507 page (milwaukeetool.com) specifically directs dipping that bit in water before each cut. That is a statement about that model, not a universal water-delivery method for every hole saw.
Do not add water around a powered tool unless the complete tool and work arrangement are approved for that use. A battery-powered tool should not be presumed suitable merely because it lacks a mains cord.
Likewise, a cutter marketed for dry operation is not automatically suitable for every material, speed or dust-control method. Read its actual instructions instead of treating wet and dry as interchangeable labels.
Starting, speed and pressure require the exact instructions
Some cutters use a pilot arrangement; others require a different approved starting method or guide. Choose the method belonging to the received accessory.
Do not invent a universal RPM or pressure for all hole sizes. Diameter, material and cutter design affect the applicable operating guidance.
Before starting on a finished installation, confirm location, access and the approved procedure. Practice on an appropriate spare piece may help with familiarity, but it does not qualify an unsuitable cutter or prove the installed wall is safe to drill.
Keep the work and tool controlled as instructed. Stop if the setup cannot be maintained, the tool is damaged or the cutting behavior calls the method into question; more force is not a substitute for resolving the cause.
Account for the whole penetration
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Plan what happens after the tile opening is complete. The pipe or fixture must still connect properly, and the surrounding waterproofing and trim detail must be finished as required.
Do not assume a neat visible edge proves the layers behind it are intact. Surface appearance and a complete installation are different checks.
Use protection and dust or water controls appropriate to the material, tool and work. Our eye-protection guide addresses another equipment decision; a bit purchase does not select the full protection plan.
Choose qualified help when the wall construction, services or required sealing detail cannot be established. The aim is a correctly located, serviceable penetration rather than simply getting the cutter through the tile.
Frequently asked questions
Does the three-piece HDG138QA kit contain three hole sizes?
No. Bosch lists one mandrel, one AutoStart pilot bit and one 1-3/8-inch hole saw.
Is the Bosch GT2000 a diamond core-bit set?
No. It is a four-piece carbide-tipped glass-and-tile bit set with small diameters.
Can I assume any glass-and-tile bit works on porcelain?
No. Confirm the exact material approval and current instructions for the specific bit.
Can I use the same wet-drilling method for every diamond cutter?
No. Follow the exact cutter’s cooling requirements and use a tool arrangement approved for that method.
Should the hole size equal the pipe’s nominal size?
Do not assume that. Use the exact fixture’s opening and clearance requirements and verify trim and sealing coverage.
How we chose
We checked current Bosch US model tables, kit contents and glass/tile bit descriptions, plus current Milwaukee model-specific cooling guidance. An older Bosch maker catalog was treated as historical context, not a complete current operating instruction. Both selected standard new Amazon.com offers showed stock with exact model and part fields on October 14, 2026. This is a source comparison, not a timed drilling, chip-out or wear test. Read our selection method and about Plumbing Picks.
Primary sources
- Bosch current diamond hole-saw kit table (maker page: www.boschtools.com/us/en/diamond-hole-saw-sets-43652-ocs-ac/): HDG138QA includes one 1-3/8-inch cutter, mandrel and pilot; confirm the current arbor arrangement.
- Bosch current glass-and-tile bit sets (maker page: www.boschtools.com/us/en/glass-tile-drill-bit-sets-43612-ocs-ac/): GT2000 has four carbide-tipped diameters and a rotary-drill format.
- Bosch current individual diamond-cutter table (maker page: www.boschtools.com/us/en/diamond-hole-saws-43883-ocs-ac/): HDG138 bare cutter compared with the kit.
- Milwaukee current 49-56-0507 page (milwaukeetool.com): that model’s water-dip instruction only; an information source.
- Bosch 2018/2019 catalog, distributor-hosted maker document (assets.unilogcorp.com): historical AutoStart and water guidance; current complete instructions still govern.