206 APPLIED MECHANICS 
should be avoided, being expensive, and*welding is not always reliable. 
Riveted and bolted joints form the best connections. Rivets and bolts 
are best placed in direct shear, but if such fastenings have to be in 
tension, bolts should be used in preference to rivets. Bolts are also gener- 
ally preferred when the diameter exceeds 1 inch. Gussets, in many 
cases, form a convenient means of attachment, particularly where many 
members meet. Care should be taken that at a joint the axes of the 
Fig. 292. 
various members intersect at a point. This is a condition which is too 
often neglected in practice. 
Sections of rafters are shown in the upper part of Fig. 292. A tee 
section is the most common form for small roofs. Double angles and 
built up sections are used for larger spans. A rafter must be of a form 
enabling it to act as a strut, and at the same time affording convenient, 
attachment ‘for the secondary members and purlins. 
At the ridge or apex the rafters are united by double gussets, which 
also form the fastening for the braces which are attached there. The 
trusses should be tied together at the apex, either by the purlins placed 
