The bayis shel rosh must have four separate compartments, and a majority of halachic authorities consider glue a connector.
Most batim makers put glue in between the four compartments of the bayis shel rosh to prevent them from opening [fig. 10.15], which could possibly affect the squareness of the bayis. In order for the bayis to be kosherlechatchila if glue is added, one of the following methods must be employed:
The glue must be less than half-way up the height of theketzitzah (rov p’rudos) [fig. 10.16].- The glue cannot reach the edges of the ketzitzah [fig. 10.17].
If both of these conditions are met, then the batim are consideredmehudar [fig. 10.18]. However, it is a higher level of hiddur not to
put any glue between the four compartments within the height of the ketzitzah (p’rudos ad hatefer) [fig. 10.19]. Those whofollow the customs of Lubavitch only use batim without glue between the compartments.