In a co-ordinate measuring machine, a linear guideway comprises two tubular guides 14, 16 mounted on a column 10 in a parallel spaced apart relation and extending in a direction parallel to the longitudinal axis of the column 10. The guides 14, 16 are mounted on the column 10 by a plurality of elongate bars 20 formed for example of carbon fibre. The bars 20 are so designed as to allow change in relative length between the guide 14 and the column 10 but to retain the guide 14 in a rigid relation to the column 10 in a direction along the axis of each of the bars 20. The guide 16 is mounted on the column 10 by a plurality of pairs of bars 50 similar to the bars 20. Each of the guides 14, 16 is anchored relative to the column 10 at one respective end. A carriage 12 is slidably mounted on the guides 14, 16 by suitable bearings and requires five degrees of restraint and one degree of freedom in the axial direction of the guides 14, 16. The guide 16 offers two degrees of restraint and the guide 14 offers one degree of restraint but, in conjunction with the guide 16 controls rotation about the axis of the latter. A bearing arrangement controls rotation about the other two axes making five restraints in total.