Ground sleeves are commonly made for square timber posts of 70×70 mm, 90×90 mm and 100×100 mm, with round-bore versions for round metal or timber poles. The internal bore fixes the post size the sleeve accepts, so measure the actual post and match it to the sleeve's inside dimension for a snug fit. A slightly loose fit is taken up by the side clamp bolts, but avoid forcing an oversized post into a smaller sleeve.

Install a drive-in ground sleeve by hammering its spike into firm soil with a driving tool, keeping the sleeve plumb, then slide the post in and tighten the side clamp bolts. A concrete-in sleeve is instead set into a wet concrete footing and left to cure before the post is fitted. In both cases the sleeve is the fixed anchor and the post is held by clamp bolts, so it can later be released and lifted out for replacement.

Ground sleeves are typically hot-dip galvanised steel, giving a thick zinc coating suited to permanent ground contact and buried use. The galvanising protects the sleeve where it is exposed to soil moisture around fence, gate and washing-line posts. Because the post sits inside the sleeve rather than in the soil, the timber base stays drier and the whole assembly generally lasts longer than a post set directly in the earth.

Yes, a ground sleeve lets you replace a post without digging out concrete, because the sleeve stays fixed in the ground and only the post is removed. Loosen the side clamp bolts, lift the old post out of the sleeve, drop the new one in and re-tighten, which makes it ideal for fence, gate and rotary washing-line posts that rot or get damaged. This is the main advantage over a post set solidly in concrete, which must be dug out to replace.