QUICK ANSWER
Match the core first, then the width, then the frame.
Core diameter decides which frame a cover can sit on. Cover width decides the cage length. End fittings and cage construction decide whether replacement covers stay compatible across a season. Nap or pile height is a separate decision about how much paint the cover carries.
Write the specification as core diameter × cover width × nap, for example 44 mm core, 230 mm (9 in) cover, 12 mm nap. This removes most sample mismatches before they reach the pallet.
CORE DIAMETER
Three core sizes cover most of the market
| Core | Approx. metric | Typical cover widths | Where it is used |
|---|---|---|---|
| 1.5 in core | ≈ 38 mm | 4, 7 and 9 in covers | Common mini and standard covers used on trim, doors and walls |
| 1.75 in core | ≈ 44 mm | 9 and 12 in covers | Widest range of covers sold into trade and retail channels |
| 2 in core | ≈ 50 mm | 9, 12 and 18 in covers | Large-surface and contractor formats where loading matters |
Labels in different markets use inches, millimetres or both. Confirm the measured core on the approved sample, because a nominal 1.5 in cover is not universally identical across suppliers.
COVER WIDTH
Width is a productivity decision, not just a size
| Width | Approx. metric | Common use |
|---|---|---|
| 4 in | ≈ 100 mm | Mini rollers, doors, trim and small repairs |
| 7 in | ≈ 180 mm | Trim, narrow walls and touch-up work |
| 9 in | ≈ 230 mm | Standard wall and ceiling painting |
| 12 in | ≈ 300 mm | Faster wall coverage on flat surfaces |
| 18 in | ≈ 460 mm | Large commercial and floor-coating work |
A wider cover covers more surface per pass but needs a frame that supports the load and a handle the user can control. Range planning usually keeps 4 in, 9 in and 12 in in stock and treats 7 in and 18 in as channel-specific additions.
FRAME FIT
Five checks before a cover is approved
Cover core vs frame cage
The cage diameter must match the cover core. A 38 mm cover will not sit correctly on a 44 mm cage.
Cover width vs cage length
Cage length is measured on the frame, not on the cover. A 9 in cover needs a 9 in cage; a partial cage leaves the cover unsupported.
Bearing and end cap
Push-on, screw-fit and quick-release frames use different end fittings. Record the type so replacement covers stay compatible.
Cage wires
4-wire and 5-wire cages differ in support and paint pickup. Keep the same specification across a range unless the difference is intentional.
Handle and frame style
Standard, heavy-duty and long-reach frames change the working position. Note the frame diameter and thread size when specifying accessories.
FAQ
Roller core questions buyers ask before sampling
What is the standard paint roller core size?
The two common core diameters are 1.5 in (≈ 38 mm) and 1.75 in (≈ 44 mm), with 2 in (≈ 50 mm) used on larger formats. The core diameter must match the frame cage; it is separate from the nap or pile height.
How do I know which roller cover fits my frame?
Check three things: core diameter, cage length and end fitting. Measure the cage rather than assuming from the cover label, and confirm the bearing type before ordering replacement covers.
Is a 9 inch roller cover measured on the cover or the frame?
The stated size normally refers to the cover width, and the frame must have a matching cage length. A short cage will not support a wider cover correctly.
Can I use a 38 mm cover on a 44 mm frame?
No. The core must match the cage diameter. Mismatched parts can slip, vibrate or fail to rotate evenly, so core diameter should be specified along with width.
How are roller widths converted to millimetres?
Approximate conversions: 4 in ≈ 100 mm, 7 in ≈ 180 mm, 9 in ≈ 230 mm, 12 in ≈ 300 mm and 18 in ≈ 460 mm. Confirm the measured dimensions on the approved sample because labels vary by market.
BUYER CHECKLIST
Information to send before sampling
- Core diameter in mm and inches, stated from a measured sample
- Cover width and required cage length
- Nap or pile height for each item in the range
- End fitting type and whether replacement covers must fit existing frames
- Carton quantity, packaging format and the market the range is sold in
NEXT STEP
Build the range around your frames.
Pamin can review covers, frames and trays together so the core sizes, widths and fittings match before a seasonal order is placed.