Abstract: In a preferred embodiment of the new and improved well tool that is described herein, a set of alternate outer tool housings are respectively arranged for carrying a common inner assembly having one or more temperature-sensitive devices. The new and improved set of alternative housings includes a first tubular housing having a solid wall of a steel of sufficient strength and thickness to withstand a predetermined pressure and a second tubular housing having inner and outer tubular members coaxially arranged to provide a hollow wall having substantially equal external and internal diameters as the first housing and which is formed of a steel of sufficiently greater strength than the steel in the first housing so that the second housing will have a design pressure rating about equal to the predetermined pressure.