Gear guide
Best pre-polish grit for rock tumbler step 3
Picked from Amazon listings, not hands-on tests. How we pick
Pre-polish (step 3, fine grit) sits between medium grit and polish, and listings do not agree on what it is. Most single-step packs are 500 silicon carbide, some are 600 silicon carbide, and a few are aluminum oxide graded 400/600 or 1000. All of them do the same job: about 7 days in a rotary barrel, until the dry stones look satin and feel silky. Cutting this step short is one of the usual reasons tumbled rocks come out dull, so it is worth buying the fine grade instead of going from medium grit straight to polish. The packs below are single-step pre-polish only. They differ in grit number, in the abrasive (silicon carbide or aluminum oxide), in weight from 1 lb to 10 lb, and in the container. Use about 2 level tablespoons per pound of rock, the same as in the earlier steps. This guide compares the listings by grit, material, weight and packaging. Nothing was tested: every detail comes from the Amazon listings. The grit calculator on this site gives exact amounts by barrel size.
Compare the picks
| Pick | Grit | Material | Weight | Container | Price | Per lb | Link |
|---|---|---|---|---|---|---|---|
 KomeStone pre-polish grit 600, step 3 refill, 5 lb | 600 | Silicon carbide | 5 lb | not stated | - | - | Amazon |
 GANGOU pre-polish grit 500, 2 lb container | 500 | Silicon carbide | 2 lb | Wide-mouth container | - | - | Amazon |
 KoolStone pre-polish grit 600, 10 lb jar | 600 | Silicon carbide | 10 lb | Jar | - | - | Amazon |
 Polly Plastics pre-polish grit 500, 1 lb (two jars) | 500 | Silicon carbide | 1 lb (2 x 0.5 lb) | Re-usable jars | - | - | Amazon |
 MJR Tumblers pre-polish 400/600 aluminum oxide, 2 lb | 400/600 | Aluminum oxide | 2 lb | not stated | - | - | Amazon |
 YHAspace pre-polish grit 500, 8 lb | 500 | Silicon carbide | 8 lb | not stated | - | - | Amazon |
 Rock Shed 1000 grit aluminum oxide, 2 lb | 1000 | Aluminum oxide | 2 lb | not stated | - | - | Amazon |
Facts are taken from each Amazon listing. Prices are checked daily and shown with their date.
If you just want one
- Closest match for the jobKomeStone pre-polish grit 600, step 3 refill, 5 lbThe listing states 600 grit silicon carbide for step 3, used after step 2 medium grinding.
- Most for the money on paperGANGOU pre-polish grit 500, 2 lb containerThe listing states 2 pounds of 500 graded silicon carbide grit, labeled pre-polish.
- Most complete listingKoolStone pre-polish grit 600, 10 lb jarThe listing states 600 grit silicon carbide pre-polish for use before the final polishing stage.
The picks in detail
Pick 1 · KomeStone
KomeStone pre-polish grit 600, step 3 refill, 5 lb
See price on AmazonA 5 lb step 3 refill of 600 grit silicon carbide. The listing gives a usage ratio, which helps when working out how many batches the pack covers.
What the listing offers
- The listing states 600 grit silicon carbide for step 3, used after step 2 medium grinding.
- Gives a usage ratio: about 1 oz of grit per pound of rocks, for up to approximately 80 lb of rocks.
- Listed as compatible with most standard rotary and vibratory rock tumblers.
Limits to know
- 5 lb of fine grit is more than a small 3 lb barrel is likely to use in a short time.
- Container type and country of origin are not stated in the listing details used for this guide.
Pick 2 · GANGOU
GANGOU pre-polish grit 500, 2 lb container
See price on Amazon2 lb of 500 graded silicon carbide for step 3 in a wide-mouth container. A small refill in the grading most four-step kits use for pre-polish.
What the listing offers
- The listing states 2 pounds of 500 graded silicon carbide grit, labeled pre-polish.
- The listing says the grit is packaged in a wide-mouth container.
- Listed for developing rocks for final polishing (step 3), with any brand of rock tumbler.
Limits to know
- No country of origin, usage amounts or instructions are given in the listing.
- Single step only: the polish for step 4 has to be bought separately.
Pick 3 · KoolStone
KoolStone pre-polish grit 600, 10 lb jar
See price on Amazon10 lb of 600 grit silicon carbide pre-polish in one jar. A bulk pack for large barrels, clubs or classrooms that run step 3 often.
What the listing offers
- The listing states 600 grit silicon carbide pre-polish for use before the final polishing stage.
- The listing says one 10 lb jar can process up to 60 pounds of rocks.
- Listed for agate, jasper, quartz, obsidian and glass, in rotary tumblers of any brand.
Limits to know
- 10 lb of step 3 grit is a large amount for a step that is run once per batch.
- No country of origin and no amount per pound of rock are given in the listing.
Pick 4 · Polly Plastics
Polly Plastics pre-polish grit 500, 1 lb (two jars)
See price on AmazonTwo 1/2 lb jars of pre-polish 500 silicon carbide grit for step 3. A small, tidy top-up for a kit that ran short on the fine grade.
What the listing offers
- The listing states two 1/2 lb jars holding 1 lb of pre-polish 500 grit in total.
- Packed in re-usable jars, which the listing says prevent spills and store unused product.
- Listed as made in the USA by an American company using American sourced materials.
Limits to know
- 1 lb in total is the smallest pack in this guide, so heavy users will reorder often.
- Single step only: coarse grit, medium grit and polish have to be bought separately.
Pick 5 · MJR Tumblers
MJR Tumblers pre-polish 400/600 aluminum oxide, 2 lb
See price on Amazon2 lb of 400/600 aluminum oxide sold as a stage 3 pre-polish. An option for anyone who wants an aluminum oxide fine step instead of 500 or 600 silicon carbide.
What the listing offers
- The listing states 400/600 grit aluminum oxide for the third stage of rock tumbling, in a 2 lb size.
- Listed as suitable for most rock tumblers, including rotary and vibratory machines.
- The listing says it is offered by a USA-based, disabled and veteran-owned company.
Limits to know
- Aluminum oxide 400/600 is not the 500 or 600 silicon carbide that most step 3 instructions name.
- The listing does not state the container type or give an amount per pound of rock.
Pick 6 · YHAspace
YHAspace pre-polish grit 500, 8 lb
See price on Amazon8 lb of 500 graded silicon carbide, labeled pre-polish and step 3. A large pack in the common kit grading for people who tumble many batches.
What the listing offers
- The listing states 8 pounds of 500 graded silicon carbide grit, labeled pre-polish.
- Listed for developing rocks for final polishing (step 3).
- Listed as compatible with any brand of rock tumbler.
Limits to know
- The listing does not describe the container or how the 8 lb is packed.
- No country of origin, usage amounts or instructions are given in the listing.
Pick 7 · Rock Shed Products
Rock Shed 1000 grit aluminum oxide, 2 lb
See price on Amazon2 lb of 1000 grit aluminum oxide, which the listing describes as an extra pre-polish for rotary and vibratory tumblers. A finer fine step, with a tip sheet included.
What the listing offers
- The title states 1000 aluminum oxide grit in a 2 lb pack.
- The listing describes it as an extra pre-polish for rotary and vibratory tumblers.
- The listing says a tip sheet and instructions are included.
Limits to know
- Described as an extra pre-polish, so it may be an added stage and not a direct swap for 500 grit.
- One bullet reads 1001 grit while the title says 1000, and the container is not stated.
Read before you buy
- Why your tumbled rocks are not shiny and how to fix each causeNine causes of dull tumbled rocks, matched to what you see on the stone, with the grit step to go back to and the fix for haze, scratches and bruises.
- Rock tumbling Petoskey stones and other soft rocksPetoskey stone is calcite, about Mohs 3, too soft for the standard recipe. Hand sanding with 220 to 600 grit is usual. A short tumbler schedule if you tumble.
- Rock tumbling grit chart: grit size, amount and time for each stageRock tumbling grit chart for all four steps: grit size, what each step does, days per step and how to tell it is done, plus about 2 tbsp of grit per pound.
Tumble Grit chooses every product independently from what its Amazon listing states. We may earn a commission from the links above. As an Amazon Associate I earn from qualifying purchases.