Quick answer
Choose a flanged Hammond 1551 when you need secure screw-down mounting or a lid that stays put; choose the plain 1551G when a compact 45 x 30 x 15 mm footprint matters more than flange mounting.
What the flange actually changes
A flanged lid gives you a wider lip that can be screwed to a panel or chassis, which helps when the enclosure will be mounted vertically or exposed to vibration. The plain 1551G has no flange, so it relies on the body itself for mounting or sits free on a desk.
Size differences that affect PCB fit
The 1551QFLBK and 1551PFLBK share a 40 x 40 mm footprint, but the P version is 20 mm tall versus 15 mm for the Q. That extra 5 mm can clear taller components or a stacked board. The 1551GBK is a different shape entirely at 45 x 30 x 15 mm, which suits narrow boards but leaves less room for wide connectors.
When the plain enclosure wins
If your board is small and you do not need panel mounting, the plain 1551G saves space and avoids the flange lip catching on other parts. It is also a sensible choice for potting because the simpler outline leaves fewer edges for potting compound to bridge.
Flanged vs plain trade-offs
- Mounting security: Pick a flanged 1551 (QFLBK or PFLBK) if the enclosure will be screwed to a panel or exposed to movement; the flange gives you a solid fixing point. Pick the plain 1551G only if the box can sit free or be fixed through the body. Check whether you need screw holes in a lip before ordering.
- Height clearance: Within the flanged 40 x 40 mm options, choose the 1551PFLBK (20 mm tall) over the 1551QFLBK (15 mm tall) when your board has tall capacitors, headers, or a stacked daughterboard. Measure your tallest component before choosing between the 15 mm and 20 mm flanged versions.
- Footprint shape: The 1551GBK is 45 x 30 mm, so it fits narrow stripboards better than the square 40 x 40 mm flanged cases, but you give up the flange mounting and the extra height of the 1551PFLBK. Lay your PCB outline on paper first; a 10 mm difference in width can rule out a case.
Product facts
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Hammond 1551QFLBK Miniature Plastic Enclosure Flanged 40 x 40 x 15 Black: Hammond 1551QFLBK is a flanged miniature plastic enclosure measuring 40 x 40 x 15 mm. The square 40 mm footprint fits small PCBs, while the 15 mm height keeps the profile low for tight builds.
Hammond 1551QFLBK Miniature Plastic Enclosure Flanged 40 x 40 x 15 Black
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Hammond 1551PFLBK Flanged Enclosure 40x40x20: Hammond 1551PFLBK is a flanged ABS enclosure measuring 40 x 40 x 20 mm. The extra 5 mm of height gives more clearance above the board than the 1551QFLBK, which helps with taller parts.
Hammond 1551PFLBK Flanged Enclosure 40x40x20
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Hammond 1551GBK Miniatureature ABS Enclosure Black 45 x 30 x 15mm: Hammond 1551GBK is a plain ABS enclosure measuring 45 x 30 x 15 mm. Its narrower 30 mm width suits slim boards, but it has no flange for screw-down panel mounting.
Which Hammond 1551 should you buy?
Best for
- Panel-mounted projects that need a screw-down flange, such as control boxes or DIN-rail adapters
- Small PCBs that fit a 40 x 40 mm footprint with up to 15 mm or 20 mm internal height
- Potting small circuits where a simple ABS box is acceptable
Not for
- Boards wider than 40 mm or longer than 45 mm, which will not fit these miniature cases
- Projects needing a plain, flange-free outline for flush mounting
- Builds that require a specific IP rating, since no ingress protection is stated for these enclosures
