A bag of 120 flat shims in six thicknesses from 1mm to 6mm. Ideal for levelling, packing and spacing during window fitting, door hanging, flooring installation and decking work.
Flat shims are one of those things you only miss when you run out of them. Whether you’re hanging a door frame, setting a window, or getting a floor perfectly level before laying hardwood, having a range of thicknesses to hand means you’re not spending ten minutes cutting bits of scrap to get a 3mm gap right. Each bag contains 120 flat shims in six thicknesses: 1mm, 2mm, 3mm, 4mm, 5mm, and 6mm, so you’ve got something for almost every situation without needing to stack a load of identical ones.
The mixed-thickness format is the practical bit. On most jobs you’ll reach for a 2mm or 3mm most of the time, but that occasional moment when you need to fine-tune a reveal or pack out a subframe to stop it rocking is exactly when a full set earns its keep. Having the full range in a single bag means less rummaging, less improvising, and fewer recuts.
Where Flat Shims Get Used on Site
Window and door fitting accounts for a big chunk of shim usage on residential and commercial projects. Getting frames plumb, square, and packed tight before fixing is straightforward when you’ve got the right thicknesses available. They’re equally useful on hardwood and laminate flooring installations, where you need consistent expansion gaps around the perimeter and a level base to lay onto. Decking builds and garden buildings are another common use, particularly when you’re shimming out posts or levelling frames on uneven ground.
Floor Levelling and Spacing
On flooring jobs specifically, flat shims like these save time at the perimeter. Rather than cutting wedge packers down, you can stack or select the right thickness and keep moving. They also work well for spacing skirting boards, packing out brackets, and any application where a precise, flat lift is needed rather than an angled one.
120 in a bag is a working quantity. You won’t be rationing them on a typical day’s fit-out, and at this price point it makes sense to keep a few bags in the van. As site consumables go, flat shims rarely get the credit they deserve, but try fitting a window without them and you’ll soon remember why they’re worth carrying.
Pro Tip: When packing window frames, start with your largest shim at the bottom and work up in small increments rather than building a tall stack of thin ones, as a stable base pack is less likely to shift when you drive fixings in.
Flat shims are used across a wide range of fitting and installation trades. Window and door installers rely on them to achieve plumb, square frames before fixing off. Floor layers use them to create consistent expansion gaps around the perimeter of hardwood and laminate installations. On decking and garden building projects, they're useful for levelling frames, packing posts, and correcting minor variations in substructures. They'll also find use in general joinery work wherever a flat, precise packer is needed.
Best For
Window and door frame fitting
Hardwood and laminate flooring installation
Decking and garden building construction
General levelling and spacing tasks
Skirting board and bracket packing
Available Thicknesses
1mm
2mm
3mm
4mm
5mm
6mm
Key Features
120 shims per bag
Six thicknesses in one pack
Flat profile for precise, stable packing
Stackable for combined thicknesses
Suitable for interior and exterior applications
Not suitable for: Not designed for structural load-bearing applications where engineered packers or metal shims would be specified. Not intended as a permanent fixing solution on their own.
Select the shim thickness that fills the gap cleanly without forcing the frame out of position. For larger gaps, stack two or more shims together rather than using a single oversized one, as this gives you more control over fine adjustments. When fitting windows and doors, place shims at hinge and locking points as a minimum, with additional packs at regular intervals along the frame. Once the frame is checked plumb and square, fix through or around the shims and trim any protruding material flush if needed.
Assess the gap or void you need to fill and estimate the thickness required
Select the appropriate shim or combination of shims from the bag
Slide the shim into position at the packing point
Check level or plumb as required and adjust shim thickness until correct
Fix the frame or component in place while holding shims in position
Trim or score off any overhanging shim material flush with the frame if required
Can these flat shims be used outdoors, for example on decking or garden buildings?
Yes, they are commonly used on decking frames and garden building construction. For permanently exposed outdoor applications it is worth checking the material specification, but for general packing during installation they are well suited to the task.
Can I stack the shims to get a thickness not included in the pack?
Absolutely. Stacking two or more shims is standard practice, so a 7mm gap, for instance, can be packed with a 4mm and a 3mm together. The flat profile means stacked shims sit stable without rocking.
These flat shims are produced in uniform flat profiles across six distinct thicknesses from 1mm to 6mm. The flat geometry ensures even load distribution across the contact area, making them reliable for packing applications where a wedge shim would cause tilting. Each bag contains 120 shims with a spread of thicknesses providing a practical working supply for most fitting and installation tasks.
Pack Quantity
120
Thicknesses Included
1mm, 2mm, 3mm, 4mm, 5mm, 6mm
Profile
Flat
Application
Levelling, packing, spacing
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